diff --git a/src-ui/app/App.jsx b/src-ui/app/App.jsx
index d645d774..7dc99689 100644
--- a/src-ui/app/App.jsx
+++ b/src-ui/app/App.jsx
@@ -9,6 +9,7 @@ import {
     UiSizeController,
     FontFamilyController,
     TransparencyController,
+    CornerRadiusController,
     PluginsController,
 } from "./_app_controllers/index.js";
 
@@ -39,6 +40,7 @@ export const App = () => {
                 <UiSizeController />
                 <FontFamilyController />
                 <TransparencyController />
+                <CornerRadiusController />
 
                 {(currentIsBackendReady.data === false || currentIsVrctAvailable.data === false)
                     ? <SplashComponent />
diff --git a/src-ui/app/_app_controllers/CornerRadiusController.jsx b/src-ui/app/_app_controllers/CornerRadiusController.jsx
new file mode 100644
index 00000000..1b84b9ad
--- /dev/null
+++ b/src-ui/app/_app_controllers/CornerRadiusController.jsx
@@ -0,0 +1,53 @@
+import { useState, useEffect } from "react";
+import { getCurrentWindow } from "@tauri-apps/api/window";
+
+export const CornerRadiusController = () => {
+    const [is_win11, setIsWin11] = useState(false);
+    const [is_maximized, setIsMaximized] = useState(false);
+
+    // OS 判定（Win11 なら platformVersion の major ≥13）
+    useEffect(() => {
+        if (navigator.userAgentData?.getHighEntropyValues) {
+            navigator.userAgentData
+                .getHighEntropyValues(["platformVersion"])
+                .then(({ platformVersion }) => {
+                    const major = parseInt(platformVersion.split(".")[0], 10);
+                    setIsWin11(major >= 13);
+                })
+                .catch(() => {
+                    setIsWin11(false);
+                })
+        } else {
+            // フォールバックで Win10 扱い
+            setIsWin11(false);
+        }
+    }, [])
+
+
+    useEffect(() => {
+        let unlisten;
+        const setup = async () => {
+            const window = await getCurrentWindow();
+            // 初期状態取得
+            setIsMaximized(await window.isMaximized());
+            // リサイズ時にも再取得
+            const updateMax = () => window.isMaximized().then(setIsMaximized);
+            unlisten = await window.listen("tauri://resize", updateMax);
+        }
+        setup();
+
+        return () => {
+            if (unlisten) {
+                unlisten();
+            }
+        }
+    }, []);
+
+    // 角丸の適用
+    useEffect(() => {
+        const radius = is_win11 && !is_maximized ? "10px" : "0";
+        document.body.style.borderRadius = radius;
+    }, [is_win11, is_maximized]);
+
+    return null;;
+}
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/index.js b/src-ui/app/_app_controllers/index.js
index d71c8b6e..ea67d783 100644
--- a/src-ui/app/_app_controllers/index.js
+++ b/src-ui/app/_app_controllers/index.js
@@ -6,4 +6,5 @@ export { ConfigPageCloseTriggerController } from "./ConfigPageCloseTriggerContro
 export { UiSizeController } from "./UiSizeController";
 export { FontFamilyController } from "./FontFamilyController";
 export { TransparencyController } from "./TransparencyController";
-export { PluginsController } from "./PluginsController";
\ No newline at end of file
+export { PluginsController } from "./PluginsController";
+export { CornerRadiusController } from "./CornerRadiusController";
\ No newline at end of file