diff --git a/firmware/README_ja.md b/firmware/README_ja.md
index 6f463741..d7140c7b 100644
--- a/firmware/README_ja.md
+++ b/firmware/README_ja.md
@@ -1,5 +1,7 @@
 # ｽﾀｯｸﾁｬﾝ ファームウェア
 
+[English](./README.md)
+
 ## 注意
 
 * ファームウェアは現在も積極的に開発中です。内部の作りやAPIが大きく変わる可能性があります。
diff --git a/firmware/docs/api.md b/firmware/docs/api.md
index 3556806d..4ceaf61b 100644
--- a/firmware/docs/api.md
+++ b/firmware/docs/api.md
@@ -1,5 +1,7 @@
 # API
 
+[日本語](./api_ja.md)
+
 The detailed API document is under construction.
 
 The source codes of Stack-chan has `TSDoc` style comments.
diff --git a/firmware/docs/api_ja.md b/firmware/docs/api_ja.md
index ccae0f0f..47344442 100644
--- a/firmware/docs/api_ja.md
+++ b/firmware/docs/api_ja.md
@@ -1,5 +1,7 @@
 # API
 
+[English](./api.md)
+
 APIの詳しいドキュメントは現在作成中です。
 
 ｽﾀｯｸﾁｬﾝのソースコードには `TSDoc` 形式のコメントがついています。
diff --git a/firmware/docs/flashing-firmware.md b/firmware/docs/flashing-firmware.md
index 2a69a4d1..1fee2eb6 100644
--- a/firmware/docs/flashing-firmware.md
+++ b/firmware/docs/flashing-firmware.md
@@ -1,5 +1,7 @@
 ## Build and flash firmware
 
+[日本語](./flashing-firmware_ja.md)
+
 ## Firmware architecture
 
 ### Host and MOD
diff --git a/firmware/docs/flashing-firmware_ja.md b/firmware/docs/flashing-firmware_ja.md
index b628de3a..153056a0 100644
--- a/firmware/docs/flashing-firmware_ja.md
+++ b/firmware/docs/flashing-firmware_ja.md
@@ -1,5 +1,7 @@
 # プログラムのビルドと書き込み
 
+[English](./flashing-firmware.md)
+
 ## ｽﾀｯｸﾁｬﾝのプログラム構成について
 
 ### ホストと MOD
diff --git a/firmware/docs/getting-started.md b/firmware/docs/getting-started.md
index 6974d84e..9fff60fc 100644
--- a/firmware/docs/getting-started.md
+++ b/firmware/docs/getting-started.md
@@ -1,5 +1,7 @@
 # Getting Started
 
+[日本語](./getting-started_ja.md)
+
 ## Prerequisites
 
 * Host PC
diff --git a/firmware/docs/getting-started_ja.md b/firmware/docs/getting-started_ja.md
index de6255fc..0ecf3e31 100644
--- a/firmware/docs/getting-started_ja.md
+++ b/firmware/docs/getting-started_ja.md
@@ -1,5 +1,7 @@
 # 環境構築
 
+[English](./getting-started.md)
+
 ## 開発に必要なもの
 
 * ホストPC
diff --git a/firmware/docs/text-to-speech.md b/firmware/docs/text-to-speech.md
index f7b5dc69..4b87bbb0 100644
--- a/firmware/docs/text-to-speech.md
+++ b/firmware/docs/text-to-speech.md
@@ -1,5 +1,7 @@
 # Using Text To Speech(TTS)
 
+[日本語](./text-to-speech_ja.md)
+
 Currently there are two way to use TTS.
 
 * __Pregenerated__: Generates and flash speeches at buildtime and plays standalone. Suitable for predefined statements.
diff --git a/firmware/docs/text-to-speech_ja.md b/firmware/docs/text-to-speech_ja.md
index 4977377f..3bf9e13c 100644
--- a/firmware/docs/text-to-speech_ja.md
+++ b/firmware/docs/text-to-speech_ja.md
@@ -1,5 +1,7 @@
 # TTS（音声合成）の使用
 
+[English](./text-to-speech.md)
+
 現在、TTSを使用するには2つの方法があります。
 
 * __事前生成__：ビルド時に音声を生成し、スタンドアロンで再生します。事前に定義された文章に適しています。