diff --git a/index.html b/index.html
index ac33af0..7c02dd0 100644
--- a/index.html
+++ b/index.html
@@ -671,29 +671,38 @@ async function tryVoicevox(text) {
     if (!apiKey) return false;
 
     const ctx = getAudioCtx();
-    const res = await fetch(TTS_API, {
-        method: 'POST',
-        headers: { 'Content-Type': 'application/json', 'Authorization': `Bearer ${apiKey}` },
-        body: JSON.stringify({ text: preprocessText(text), speaker: ttsSpeaker }),
-    });
-    if (!res.ok) {
-        const msg = res.status === 401 ? 'APIキーが無効です' : res.status === 503 ? 'VOICEVOXが起動していません' : `サーバーエラー (${res.status})`;
-        if (currentIdx === 0 && typeof showToast === 'function') showToast('VOICEVOX: ' + msg);
-        return false;
+    for (let attempt = 0; attempt < 4; attempt++) {
+        if (attempt > 0) await new Promise(r => setTimeout(r, 2000 * attempt));
+        const res = await fetch(TTS_API, {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json', 'Authorization': `Bearer ${apiKey}` },
+            body: JSON.stringify({ text: preprocessText(text), speaker: ttsSpeaker }),
+        });
+        if (res.status === 503) {
+            const body = await res.json().catch(() => ({}));
+            if (body.error === 'TTS_BUSY' && attempt < 3) continue; // 自動リトライ
+            const msg = body.error === 'TTS_BUSY' ? 'サーバーが混雑しています' : 'VOICEVOXが起動していません';
+            if (currentIdx === 0 && typeof showToast === 'function') showToast('VOICEVOX: ' + msg);
+            return false;
+        }
+        if (!res.ok) {
+            const msg = res.status === 401 ? 'APIキーが無効です' : `サーバーエラー (${res.status})`;
+            if (currentIdx === 0 && typeof showToast === 'function') showToast('VOICEVOX: ' + msg);
+            return false;
+        }
+        const buf = await ctx.decodeAudioData(await res.arrayBuffer());
+        if (!isPlaying) return true;
+        return new Promise(resolve => {
+            currentSource = ctx.createBufferSource();
+            currentSource.buffer = buf;
+            currentSource.playbackRate.value = speechRate;
+            currentSource.connect(ctx.destination);
+            currentSource.onended = () => { currentSource = null; resolve(true); };
+            currentSource.start(0);
+            updateVoiceBadge(true);
+        });
     }
-
-    const buf = await ctx.decodeAudioData(await res.arrayBuffer());
-    if (!isPlaying) return true;
-
-    return new Promise(resolve => {
-        currentSource = ctx.createBufferSource();
-        currentSource.buffer = buf;
-        currentSource.playbackRate.value = speechRate;
-        currentSource.connect(ctx.destination);
-        currentSource.onended = () => { currentSource = null; resolve(true); };
-        currentSource.start(0);
-        updateVoiceBadge(true);
-    });
+    return false;
 }
 
 function speakBrowser(text, onEnd) {