diff --git a/apps/client/src/scenes/game/input/joystick/JoystickCoordinator.tsx b/apps/client/src/scenes/game/input/joystick/JoystickCoordinator.tsx
index 253cc64..da830ac 100644
--- a/apps/client/src/scenes/game/input/joystick/JoystickCoordinator.tsx
+++ b/apps/client/src/scenes/game/input/joystick/JoystickCoordinator.tsx
@@ -6,7 +6,7 @@
 import { useCallback } from "react";
 import type React from "react";
 import { JoystickView } from "./JoystickView";
-import type { NormalizedInput } from "./joystick.types";
+import type { NormalizedInput } from "./common";
 import { useJoystick } from "./useJoystick";
 
 /** JoystickCoordinator が提供する描画用データと入力ハンドラ */
diff --git a/apps/client/src/scenes/game/input/joystick/JoystickInputLayer.tsx b/apps/client/src/scenes/game/input/joystick/JoystickInputLayer.tsx
index 37bce33..b634672 100644
--- a/apps/client/src/scenes/game/input/joystick/JoystickInputLayer.tsx
+++ b/apps/client/src/scenes/game/input/joystick/JoystickInputLayer.tsx
@@ -6,7 +6,7 @@
 import { JoystickCoordinator } from "./JoystickCoordinator";
 
 /** 入力半径の既定値を外部から参照できるように再公開 */
-export { MAX_DIST } from "./joystick.constants";
+export { MAX_DIST } from "./common";
 
 /** JoystickInputLayer の入力コールバック */
 type Props = {
diff --git a/apps/client/src/scenes/game/input/joystick/JoystickModel.ts b/apps/client/src/scenes/game/input/joystick/JoystickModel.ts
new file mode 100644
index 0000000..06193f5
--- /dev/null
+++ b/apps/client/src/scenes/game/input/joystick/JoystickModel.ts
@@ -0,0 +1,38 @@
+/**
+ * JoystickModel
+ * ジョイスティック入力の座標計算を担うモデル
+ * ノブ表示オフセットと正規化入力ベクトルを算出する
+ */
+import type { NormalizedInput, Point } from './common';
+
+/** ジョイスティック計算結果を表す型 */
+export type JoystickComputed = {
+  knobOffset: Point;
+  normalized: NormalizedInput;
+};
+
+/** 座標差分からノブオフセットと正規化入力を計算する */
+export const computeJoystick = (
+  center: Point,
+  current: Point,
+  radius: number
+): JoystickComputed => {
+  const safeRadius = radius > 0 ? radius : 1;
+
+  const dx = current.x - center.x;
+  const dy = current.y - center.y;
+  const dist = Math.hypot(dx, dy);
+  const angle = Math.atan2(dy, dx);
+
+  const limitedDist = Math.min(dist, safeRadius);
+  const offsetX = Math.cos(angle) * limitedDist;
+  const offsetY = Math.sin(angle) * limitedDist;
+
+  return {
+    knobOffset: { x: offsetX, y: offsetY },
+    normalized: {
+      x: offsetX / safeRadius,
+      y: offsetY / safeRadius,
+    },
+  };
+};
diff --git a/apps/client/src/scenes/game/input/joystick/JoystickView.tsx b/apps/client/src/scenes/game/input/joystick/JoystickView.tsx
index ef316d9..cf6db61 100644
--- a/apps/client/src/scenes/game/input/joystick/JoystickView.tsx
+++ b/apps/client/src/scenes/game/input/joystick/JoystickView.tsx
@@ -3,7 +3,7 @@
  * ジョイスティックの見た目だけを描画するコンポーネント
  * 入力処理は持たず，受け取った座標情報をもとにUIを描く
  */
-import type { Point } from "./joystick.types";
+import type { Point } from "./common";
 
 /** 表示に必要な座標と状態 */
 type Props = {
diff --git a/apps/client/src/scenes/game/input/joystick/common/index.ts b/apps/client/src/scenes/game/input/joystick/common/index.ts
new file mode 100644
index 0000000..2c0838b
--- /dev/null
+++ b/apps/client/src/scenes/game/input/joystick/common/index.ts
@@ -0,0 +1,5 @@
+/** 共有型を再公開する */
+export type { NormalizedInput, Point } from './joystick.types';
+
+/** 共有定数を再公開する */
+export { MAX_DIST } from './joystick.constants';
diff --git a/apps/client/src/scenes/game/input/joystick/common/joystick.constants.ts b/apps/client/src/scenes/game/input/joystick/common/joystick.constants.ts
new file mode 100644
index 0000000..88b2d7b
--- /dev/null
+++ b/apps/client/src/scenes/game/input/joystick/common/joystick.constants.ts
@@ -0,0 +1,8 @@
+/**
+ * joystick.constants
+ * ジョイスティック入力に関する定数をまとめる
+ * 共有する半径の既定値などを定義する
+ */
+
+/** UI側と共有する最大半径の既定値 */
+export const MAX_DIST = 60;
diff --git a/apps/client/src/scenes/game/input/joystick/common/joystick.types.ts b/apps/client/src/scenes/game/input/joystick/common/joystick.types.ts
new file mode 100644
index 0000000..d55577e
--- /dev/null
+++ b/apps/client/src/scenes/game/input/joystick/common/joystick.types.ts
@@ -0,0 +1,11 @@
+/**
+ * joystick.types
+ * ジョイスティック入力で使う型をまとめる
+ * 座標や入力の共通表現を定義する
+ */
+
+/** 2D座標の簡易型 */
+export type Point = { x: number; y: number };
+
+/** 正規化された入力ベクトル */
+export type NormalizedInput = { x: number; y: number };
diff --git a/apps/client/src/scenes/game/input/joystick/joystick.constants.ts b/apps/client/src/scenes/game/input/joystick/joystick.constants.ts
deleted file mode 100644
index 88b2d7b..0000000
--- a/apps/client/src/scenes/game/input/joystick/joystick.constants.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-/**
- * joystick.constants
- * ジョイスティック入力に関する定数をまとめる
- * 共有する半径の既定値などを定義する
- */
-
-/** UI側と共有する最大半径の既定値 */
-export const MAX_DIST = 60;
diff --git a/apps/client/src/scenes/game/input/joystick/joystick.types.ts b/apps/client/src/scenes/game/input/joystick/joystick.types.ts
deleted file mode 100644
index d55577e..0000000
--- a/apps/client/src/scenes/game/input/joystick/joystick.types.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-/**
- * joystick.types
- * ジョイスティック入力で使う型をまとめる
- * 座標や入力の共通表現を定義する
- */
-
-/** 2D座標の簡易型 */
-export type Point = { x: number; y: number };
-
-/** 正規化された入力ベクトル */
-export type NormalizedInput = { x: number; y: number };
diff --git a/apps/client/src/scenes/game/input/joystick/useJoystick.ts b/apps/client/src/scenes/game/input/joystick/useJoystick.ts
index c514fbc..50021da 100644
--- a/apps/client/src/scenes/game/input/joystick/useJoystick.ts
+++ b/apps/client/src/scenes/game/input/joystick/useJoystick.ts
@@ -5,8 +5,9 @@
  */
 import { useCallback, useState } from "react";
 import type React from "react";
-import { MAX_DIST } from "./joystick.constants";
-import type { NormalizedInput, Point } from "./joystick.types";
+import { MAX_DIST } from "./common";
+import { computeJoystick } from "./JoystickModel";
+import type { NormalizedInput, Point } from "./common";
 
 /** フックに渡す設定 */
 type Props = {
@@ -59,19 +60,9 @@
       const point = getClientPoint(e);
       if (!point) return null;
 
-      const dx = point.x - center.x;
-      const dy = point.y - center.y;
-      const dist = Math.sqrt(dx * dx + dy * dy);
-      const angle = Math.atan2(dy, dx);
-
-      const limitedDist = Math.min(dist, radius);
-      const offsetX = Math.cos(angle) * limitedDist;
-      const offsetY = Math.sin(angle) * limitedDist;
-      const normalizedX = offsetX / radius;
-      const normalizedY = offsetY / radius;
-
-      setKnobOffset({ x: offsetX, y: offsetY });
-      return { x: normalizedX, y: normalizedY };
+      const computed = computeJoystick(center, point, radius);
+      setKnobOffset(computed.knobOffset);
+      return computed.normalized;
     },
     [isMoving, center.x, center.y, radius]
   );