diff --git a/.nuget/NuGet.Config b/.nuget/NuGet.Config
deleted file mode 100644
index 67f8ea0..0000000
--- a/.nuget/NuGet.Config
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<configuration>
-  <solution>
-    <add key="disableSourceControlIntegration" value="true" />
-  </solution>
-</configuration>
\ No newline at end of file
diff --git a/.nuget/NuGet.exe b/.nuget/NuGet.exe
deleted file mode 100644
index c41a0d0..0000000
Binary files a/.nuget/NuGet.exe and /dev/null differ
diff --git a/.nuget/NuGet.targets b/.nuget/NuGet.targets
deleted file mode 100644
index 3f8c37b..0000000
--- a/.nuget/NuGet.targets
+++ /dev/null
@@ -1,144 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-    <PropertyGroup>
-        <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">$(MSBuildProjectDirectory)\..\</SolutionDir>
-
-        <!-- Enable the restore command to run before builds -->
-        <RestorePackages Condition="  '$(RestorePackages)' == '' ">false</RestorePackages>
-
-        <!-- Property that enables building a package from a project -->
-        <BuildPackage Condition=" '$(BuildPackage)' == '' ">false</BuildPackage>
-
-        <!-- Determines if package restore consent is required to restore packages -->
-        <RequireRestoreConsent Condition=" '$(RequireRestoreConsent)' != 'false' ">true</RequireRestoreConsent>
-
-        <!-- Download NuGet.exe if it does not already exist -->
-        <DownloadNuGetExe Condition=" '$(DownloadNuGetExe)' == '' ">false</DownloadNuGetExe>
-    </PropertyGroup>
-
-    <ItemGroup Condition=" '$(PackageSources)' == '' ">
-        <!-- Package sources used to restore packages. By default, registered sources under %APPDATA%\NuGet\NuGet.Config will be used -->
-        <!-- The official NuGet package source (https://www.nuget.org/api/v2/) will be excluded if package sources are specified and it does not appear in the list -->
-        <!--
-            <PackageSource Include="https://www.nuget.org/api/v2/" />
-            <PackageSource Include="https://my-nuget-source/nuget/" />
-        -->
-    </ItemGroup>
-
-    <PropertyGroup Condition=" '$(OS)' == 'Windows_NT'">
-        <!-- Windows specific commands -->
-        <NuGetToolsPath>$([System.IO.Path]::Combine($(SolutionDir), ".nuget"))</NuGetToolsPath>
-    </PropertyGroup>
-
-    <PropertyGroup Condition=" '$(OS)' != 'Windows_NT'">
-        <!-- We need to launch nuget.exe with the mono command if we're not on windows -->
-        <NuGetToolsPath>$(SolutionDir).nuget</NuGetToolsPath>
-    </PropertyGroup>
-
-    <PropertyGroup>
-        <PackagesProjectConfig Condition=" '$(OS)' == 'Windows_NT'">$(MSBuildProjectDirectory)\packages.$(MSBuildProjectName.Replace(' ', '_')).config</PackagesProjectConfig>
-        <PackagesProjectConfig Condition=" '$(OS)' != 'Windows_NT'">$(MSBuildProjectDirectory)\packages.$(MSBuildProjectName).config</PackagesProjectConfig>
-    </PropertyGroup>
-
-    <PropertyGroup>
-      <PackagesConfig Condition="Exists('$(MSBuildProjectDirectory)\packages.config')">$(MSBuildProjectDirectory)\packages.config</PackagesConfig>
-      <PackagesConfig Condition="Exists('$(PackagesProjectConfig)')">$(PackagesProjectConfig)</PackagesConfig>
-    </PropertyGroup>
-    
-    <PropertyGroup>
-        <!-- NuGet command -->
-        <NuGetExePath Condition=" '$(NuGetExePath)' == '' ">$(NuGetToolsPath)\NuGet.exe</NuGetExePath>
-        <PackageSources Condition=" $(PackageSources) == '' ">@(PackageSource)</PackageSources>
-
-        <NuGetCommand Condition=" '$(OS)' == 'Windows_NT'">"$(NuGetExePath)"</NuGetCommand>
-        <NuGetCommand Condition=" '$(OS)' != 'Windows_NT' ">mono --runtime=v4.0.30319 "$(NuGetExePath)"</NuGetCommand>
-
-        <PackageOutputDir Condition="$(PackageOutputDir) == ''">$(TargetDir.Trim('\\'))</PackageOutputDir>
-
-        <RequireConsentSwitch Condition=" $(RequireRestoreConsent) == 'true' ">-RequireConsent</RequireConsentSwitch>
-        <NonInteractiveSwitch Condition=" '$(VisualStudioVersion)' != '' AND '$(OS)' == 'Windows_NT' ">-NonInteractive</NonInteractiveSwitch>
-
-        <PaddedSolutionDir Condition=" '$(OS)' == 'Windows_NT'">"$(SolutionDir) "</PaddedSolutionDir>
-        <PaddedSolutionDir Condition=" '$(OS)' != 'Windows_NT' ">"$(SolutionDir)"</PaddedSolutionDir>
-
-        <!-- Commands -->
-        <RestoreCommand>$(NuGetCommand) install "$(PackagesConfig)" -source "$(PackageSources)"  $(NonInteractiveSwitch) $(RequireConsentSwitch) -solutionDir $(PaddedSolutionDir)</RestoreCommand>
-        <BuildCommand>$(NuGetCommand) pack "$(ProjectPath)" -Properties "Configuration=$(Configuration);Platform=$(Platform)" $(NonInteractiveSwitch) -OutputDirectory "$(PackageOutputDir)" -symbols</BuildCommand>
-
-        <!-- We need to ensure packages are restored prior to assembly resolve -->
-        <BuildDependsOn Condition="$(RestorePackages) == 'true'">
-            RestorePackages;
-            $(BuildDependsOn);
-        </BuildDependsOn>
-
-        <!-- Make the build depend on restore packages -->
-        <BuildDependsOn Condition="$(BuildPackage) == 'true'">
-            $(BuildDependsOn);
-            BuildPackage;
-        </BuildDependsOn>
-    </PropertyGroup>
-
-    <Target Name="CheckPrerequisites">
-        <!-- Raise an error if we're unable to locate nuget.exe  -->
-        <Error Condition="'$(DownloadNuGetExe)' != 'true' AND !Exists('$(NuGetExePath)')" Text="Unable to locate '$(NuGetExePath)'" />
-        <!--
-        Take advantage of MsBuild's build dependency tracking to make sure that we only ever download nuget.exe once.
-        This effectively acts as a lock that makes sure that the download operation will only happen once and all
-        parallel builds will have to wait for it to complete.
-        -->
-        <MsBuild Targets="_DownloadNuGet" Projects="$(MSBuildThisFileFullPath)" Properties="Configuration=NOT_IMPORTANT;DownloadNuGetExe=$(DownloadNuGetExe)" />
-    </Target>
-
-    <Target Name="_DownloadNuGet">
-        <DownloadNuGet OutputFilename="$(NuGetExePath)" Condition=" '$(DownloadNuGetExe)' == 'true' AND !Exists('$(NuGetExePath)')" />
-    </Target>
-
-    <Target Name="RestorePackages" DependsOnTargets="CheckPrerequisites">        
-        <Exec Command="$(RestoreCommand)"
-              Condition="'$(OS)' != 'Windows_NT' And Exists('$(PackagesConfig)')" />
-
-        <Exec Command="$(RestoreCommand)"
-              LogStandardErrorAsError="true"
-              Condition="'$(OS)' == 'Windows_NT' And Exists('$(PackagesConfig)')" />
-    </Target>
-
-    <Target Name="BuildPackage" DependsOnTargets="CheckPrerequisites">
-        <Exec Command="$(BuildCommand)"
-              Condition=" '$(OS)' != 'Windows_NT' " />
-
-        <Exec Command="$(BuildCommand)"
-              LogStandardErrorAsError="true"
-              Condition=" '$(OS)' == 'Windows_NT' " />
-    </Target>
-
-    <UsingTask TaskName="DownloadNuGet" TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
-        <ParameterGroup>
-            <OutputFilename ParameterType="System.String" Required="true" />
-        </ParameterGroup>
-        <Task>
-            <Reference Include="System.Core" />
-            <Using Namespace="System" />
-            <Using Namespace="System.IO" />
-            <Using Namespace="System.Net" />
-            <Using Namespace="Microsoft.Build.Framework" />
-            <Using Namespace="Microsoft.Build.Utilities" />
-            <Code Type="Fragment" Language="cs">
-                <![CDATA[
-                try {
-                    OutputFilename = Path.GetFullPath(OutputFilename);
-
-                    Log.LogMessage("Downloading latest version of NuGet.exe...");
-                    WebClient webClient = new WebClient();
-                    webClient.DownloadFile("https://www.nuget.org/nuget.exe", OutputFilename);
-
-                    return true;
-                }
-                catch (Exception ex) {
-                    Log.LogErrorFromException(ex);
-                    return false;
-                }
-            ]]>
-            </Code>
-        </Task>
-    </UsingTask>
-</Project>
diff --git a/VoiceTextWebAPI.Client.sln b/VoiceTextWebAPI.Client.sln
index 61550e7..06ba294 100644
--- a/VoiceTextWebAPI.Client.sln
+++ b/VoiceTextWebAPI.Client.sln
@@ -1,16 +1,9 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 2013
-VisualStudioVersion = 12.0.30723.0
+# Visual Studio 15
+VisualStudioVersion = 15.0.27428.2005
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = ".nuget", ".nuget", "{8A7F64CF-F75B-493F-A32A-84D378BF7113}"
-	ProjectSection(SolutionItems) = preProject
-		.nuget\NuGet.Config = .nuget\NuGet.Config
-		.nuget\NuGet.exe = .nuget\NuGet.exe
-		.nuget\NuGet.targets = .nuget\NuGet.targets
-	EndProjectSection
-EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "VoiceTextWebAPI.Client", "VoiceTextWebAPI.Client\VoiceTextWebAPI.Client.csproj", "{4359A4B5-6122-4B18-A72B-905BC380C46D}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "VoiceTextWebAPI.Client", "VoiceTextWebAPI.Client\VoiceTextWebAPI.Client.csproj", "{4359A4B5-6122-4B18-A72B-905BC380C46D}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Documents", "Documents", "{06BF0E03-243F-48CA-9B5E-00C4EACAED84}"
 	ProjectSection(SolutionItems) = preProject
@@ -32,4 +25,7 @@ Global
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {B3BB0C31-C004-48B3-A333-0A483373813D}
+	EndGlobalSection
 EndGlobal
diff --git a/VoiceTextWebAPI.Client/Properties/AssemblyInfo.cs b/VoiceTextWebAPI.Client/Properties/AssemblyInfo.cs
deleted file mode 100644
index 3743ebe..0000000
--- a/VoiceTextWebAPI.Client/Properties/AssemblyInfo.cs
+++ /dev/null
@@ -1,35 +0,0 @@
-using System.Reflection;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-// General Information about an assembly is controlled through the following 
-// set of attributes. Change these attribute values to modify the information
-// associated with an assembly.
-[assembly: AssemblyTitle("VoiceTextWebAPI.Client")]
-[assembly: AssemblyDescription("")]
-[assembly: AssemblyConfiguration("")]
-[assembly: AssemblyCompany("")]
-[assembly: AssemblyProduct(".NET Client for VoiceText Web API")]
-[assembly: AssemblyCopyright("Copyright © J.Sakamoto 2014-2018, MIT License")]
-[assembly: AssemblyTrademark("")]
-[assembly: AssemblyCulture("")]
-
-// Setting ComVisible to false makes the types in this assembly not visible 
-// to COM components.  If you need to access a type in this assembly from 
-// COM, set the ComVisible attribute to true on that type.
-[assembly: ComVisible(false)]
-
-// The following GUID is for the ID of the typelib if this project is exposed to COM
-[assembly: Guid("731cf40d-d365-4c5b-9d47-f7e5cbbefb1d")]
-
-// Version information for an assembly consists of the following four values:
-//
-//      Major Version
-//      Minor Version 
-//      Build Number
-//      Revision
-//
-// You can specify all the values or you can default the Build and Revision Numbers 
-// by using the '*' as shown below:
-// [assembly: AssemblyVersion("1.0.*")]
-[assembly: AssemblyVersion("2.0.0.0")]
diff --git a/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.csproj b/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.csproj
index 8915598..0f9d281 100644
--- a/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.csproj
+++ b/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.csproj
@@ -1,75 +1,35 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProjectGuid>{4359A4B5-6122-4B18-A72B-905BC380C46D}</ProjectGuid>
-    <OutputType>Library</OutputType>
-    <AppDesignerFolder>Properties</AppDesignerFolder>
-    <RootNamespace>VoiceTextWebAPI.Client</RootNamespace>
-    <AssemblyName>VoiceTextWebAPI.Client</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
-    <FileAlignment>512</FileAlignment>
-    <TargetFrameworkProfile />
+    <TargetFrameworks>netstandard2.0;net45</TargetFrameworks>
+    <NoWarn>$(NoWarn);1591</NoWarn>
+    <GeneratePackageOnBuild Condition="'$(Configuration)' == 'Release'">true</GeneratePackageOnBuild>
+    <Authors>J.Sakamoto</Authors>
+    <Version>2.0.0.1</Version>
+    <Description>This library is the client of [HOYA Voice Text Web API](https://cloud.voicetext.jp/webapi) for .NET.</Description>
+    <Copyright>Copyright © J.Sakamoto 2014-2018, MIT License</Copyright>
+    <Product>.NET Client for VoiceText Web API</Product>
+    <PackageLicenseUrl>https://github.com/jsakamoto/voicetext-webapi-client4net/blob/master/LICENSE</PackageLicenseUrl>
+    <PackageProjectUrl>https://github.com/jsakamoto/voicetext-webapi-client4net</PackageProjectUrl>
+    <RepositoryUrl></RepositoryUrl>
+    <PackageTags>voicetext,voice,speach</PackageTags>
+    <PackageReleaseNotes>v.2.0.0.1
+- support .NET Standard 2.0
+v.2.0
+- [Breaking Change] Remove aac format. 
+v.1.4
+- Add mp3 format.
+v.1.3
+- Can chose voice file format from wav/ogg/aac.
+v.1.2
+- Add speaker "Bear"(Berserk Bear)!
+v.1.1
+- Add speaker "Santa"(Santa Claus)!
+v.1.0
+- First release.
+</PackageReleaseNotes>
   </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
-    <OutputPath>bin\Debug\</OutputPath>
-    <DefineConstants>DEBUG;TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <Prefer32Bit>false</Prefer32Bit>
-  </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <DebugType>pdbonly</DebugType>
-    <Optimize>true</Optimize>
-    <OutputPath>bin\Release\</OutputPath>
-    <DefineConstants>TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <Prefer32Bit>false</Prefer32Bit>
-  </PropertyGroup>
-  <PropertyGroup>
-    <RunPostBuildEvent>OnBuildSuccess</RunPostBuildEvent>
-  </PropertyGroup>
-  <ItemGroup>
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="Microsoft.CSharp" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'net45'">
     <Reference Include="System.Net.Http" />
     <Reference Include="System.Runtime.Serialization" />
-    <Reference Include="System.XML" />
   </ItemGroup>
-  <ItemGroup>
-    <Compile Include="Emotion.cs" />
-    <Compile Include="EmotionLevel.cs" />
-    <Compile Include="Format.cs" />
-    <Compile Include="Speaker.cs" />
-    <Compile Include="VoiceTextClient.cs" />
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="VoiceTextErrorResponse.cs" />
-    <Compile Include="VoiceTextException.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <None Include="VoiceTextWebAPI.Client.nuspec" />
-  </ItemGroup>
-  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
-  <PropertyGroup>
-    <PostBuildEvent>if "$(ConfigurationName)" == "Release" goto PACK
-goto END
-:PACK
-pushd "$(ProjectDir)"
-"$(SolutionDir).nuget\nuget.exe" pack "$(ProjectPath)" -Prop Configuration=Release;Platform=AnyCPU -o $(OutDir)
-:END</PostBuildEvent>
-  </PropertyGroup>
-  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
-       Other similar extension points exist, see Microsoft.Common.targets.
-  <Target Name="BeforeBuild">
-  </Target>
-  <Target Name="AfterBuild">
-  </Target>
-  -->
-</Project>
\ No newline at end of file
+</Project>
diff --git a/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.nuspec b/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.nuspec
deleted file mode 100644
index c953c71..0000000
--- a/VoiceTextWebAPI.Client/VoiceTextWebAPI.Client.nuspec
+++ /dev/null
@@ -1,37 +0,0 @@
-<?xml version="1.0"?>
-<package >
-  <metadata>
-    <id>$id$</id>
-    <version>$version$</version>
-    <title>$title$</title>
-    <authors>J.Sakamoto</authors>
-    <owners>J.Sakamoto</owners>
-    <licenseUrl>https://github.com/jsakamoto/voicetext-webapi-client4net/blob/master/LICENSE</licenseUrl>
-    <projectUrl>https://github.com/jsakamoto/voicetext-webapi-client4net</projectUrl>
-    <!--
-    <iconUrl/>
-    -->
-    <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <summary>The Web API client of [HOYA Voice Text Web API](https://cloud.voicetext.jp/webapi) for .NET</summary>
-    <description>
-      This library is the client of [HOYA Voice Text Web API](https://cloud.voicetext.jp/webapi) for .NET.
-    </description>
-    <releaseNotes>
-      <![CDATA[
-      v.2.0
-      - [Breaking Change] Remove aac format. 
-      v.1.4
-      - Add mp3 format.
-      v.1.3
-      - Can chose voice file format from wav/ogg/aac.
-      v.1.2
-      - Add speaker "Bear"(Berserk Bear)!
-      v.1.1
-      - Add speaker "Santa"(Santa Claus)!
-      v.1.0
-      - First release.
-      ]]>
-    </releaseNotes>
-    <tags>voicetext,voice,speach</tags>
-  </metadata>
-</package>