diff --git a/services/tts.ts b/services/tts.ts
index babac7b..abb3351 100644
--- a/services/tts.ts
+++ b/services/tts.ts
@@ -1,5 +1,6 @@
 import fs from "fs";
 import path from "path";
+import ffmpeg from "fluent-ffmpeg";
 
 // VOICEVOX APIの設定
 const VOICEVOX_HOST = import.meta.env["VOICEVOX_HOST"];
@@ -61,10 +62,29 @@ export async function generateTTS(
     fs.mkdirSync(outputDir, { recursive: true });
   }
 
-  const filePath = path.resolve(outputDir, `${itemId}.wav`); // Use the provided filename directly
-  console.log(`音声ファイル保存開始: ${filePath}`);
-  fs.writeFileSync(filePath, audioBuffer);
-  console.log(`音声ファイル保存完了: ${filePath}`);
+  const wavFilePath = path.resolve(outputDir, `${itemId}.wav`);
+  const mp3FilePath = path.resolve(outputDir, `${itemId}.mp3`);
 
-  return path.basename(filePath);
+  console.log(`WAVファイル保存開始: ${wavFilePath}`);
+  fs.writeFileSync(wavFilePath, audioBuffer);
+  console.log(`WAVファイル保存完了: ${wavFilePath}`);
+
+  console.log(`MP3変換開始: ${wavFilePath} -> ${mp3FilePath}`);
+  await new Promise<void>((resolve, reject) => {
+    ffmpeg(wavFilePath)
+      .audioCodec("libmp3lame")
+      .format("mp3")
+      .on("end", () => {
+        console.log(`MP3変換完了: ${mp3FilePath}`);
+        fs.unlinkSync(wavFilePath); // WAVファイルを削除
+        resolve();
+      })
+      .on("error", (err) => {
+        console.error(`MP3変換エラー: ${err.message}`);
+        reject(err);
+      })
+      .save(mp3FilePath);
+  });
+
+  return path.basename(mp3FilePath);
 }