diff --git a/firmware/firmware.ino b/firmware/firmware.ino
index e1a465a..f0cd2a1 100644
--- a/firmware/firmware.ino
+++ b/firmware/firmware.ino
@@ -12,10 +12,12 @@ const uint32_t ws2812bColors[] = {
   0x0000FF, 0x4B0082, 0x8F00FF
 };
 constexpr uint8_t WS2812B_COLOR_COUNT = sizeof(ws2812bColors) / sizeof(ws2812bColors[0]);
-constexpr unsigned long WS2812B_INTERVAL_MS = 500;
+constexpr unsigned long WS2812B_INTERVAL_MS = 30;
+constexpr unsigned long WS2812B_TRANSITION_MS = 3000;
 bool isPlaying = false;
 uint8_t ws2812bColorIndex = 0;
 unsigned long lastWs2812bUpdate = 0;
+unsigned long ws2812bTransitionStart = 0;
 
 // I2C接続のOLED設定 (SSD1306 128x64)
 U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
@@ -89,9 +91,14 @@ void volume_changed_callback(int volume) {
   updateDisplay();
 }
 
-void audio_state_changed_callback(esp_a2d_audio_state_t state) {
+void audio_state_changed_callback(esp_a2d_audio_state_t state, void *) {
   isPlaying = (state == ESP_A2D_AUDIO_STATE_STARTED);
 
+  if (isPlaying) {
+    ws2812bTransitionStart = millis();
+    lastWs2812bUpdate = ws2812bTransitionStart;
+  }
+
   if (!isPlaying) {
     ws2812bColorIndex = 3;
     ws2812b.setPixelColor(0, ws2812bColors[ws2812bColorIndex]);
@@ -145,9 +152,26 @@ void setup() {
 
 void loop() {
   if (isPlaying && millis() - lastWs2812bUpdate >= WS2812B_INTERVAL_MS) {
-    lastWs2812bUpdate = millis();
-    ws2812bColorIndex = (ws2812bColorIndex + 1) % WS2812B_COLOR_COUNT;
-    ws2812b.setPixelColor(0, ws2812bColors[ws2812bColorIndex]);
+    unsigned long now = millis();
+    lastWs2812bUpdate = now;
+    unsigned long transitionElapsed = now - ws2812bTransitionStart;
+    if (transitionElapsed >= WS2812B_TRANSITION_MS) {
+      ws2812bColorIndex = (ws2812bColorIndex + transitionElapsed / WS2812B_TRANSITION_MS)
+        % WS2812B_COLOR_COUNT;
+      ws2812bTransitionStart = now;
+      transitionElapsed = 0;
+    }
+    uint8_t nextColorIndex = (ws2812bColorIndex + 1) % WS2812B_COLOR_COUNT;
+    uint32_t currentColor = ws2812bColors[ws2812bColorIndex];
+    uint32_t nextColor = ws2812bColors[nextColorIndex];
+    uint8_t red = ((currentColor >> 16) * (WS2812B_TRANSITION_MS - transitionElapsed)
+      + (nextColor >> 16) * transitionElapsed) / WS2812B_TRANSITION_MS;
+    uint8_t green = (((currentColor >> 8) & 0xFF) * (WS2812B_TRANSITION_MS - transitionElapsed)
+      + ((nextColor >> 8) & 0xFF) * transitionElapsed) / WS2812B_TRANSITION_MS;
+    uint8_t blue = ((currentColor & 0xFF) * (WS2812B_TRANSITION_MS - transitionElapsed)
+      + (nextColor & 0xFF) * transitionElapsed) / WS2812B_TRANSITION_MS;
+    ws2812b.setPixelColor(0, red, green, blue);
     ws2812b.show();
+
   }
 }
\ No newline at end of file