diff --git a/package-lock.json b/package-lock.json
index e0836596..9255bcff 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@next2d/player",
-  "version": "3.8.0",
+  "version": "3.8.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@next2d/player",
-      "version": "3.8.0",
+      "version": "3.8.1",
       "license": "MIT",
       "workspaces": [
         "packages/*"
@@ -3276,9 +3276,9 @@
       "license": "MIT"
     },
     "node_modules/nanoid": {
-      "version": "3.3.13",
-      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.13.tgz",
-      "integrity": "sha512-sPdqC6ByMVVGvF1ynvvMo0/o+oD1VX7DaHhijt1bFgjvBkHBib4t49GoNDhf2NDta4oeUNlaGbSt5K7qjZ955Q==",
+      "version": "3.3.14",
+      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.14.tgz",
+      "integrity": "sha512-U9kYi5bpVMEI31yC8iw4bJJp0avcHXA0W8/wNfLfnvJYzihQo2ZRPYPvpAAd570HAcCBjCTN7vnr+v4StKl1IQ==",
       "dev": true,
       "funding": [
         {
diff --git a/package.json b/package.json
index 02167e97..ff47c482 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@next2d/player",
-  "version": "3.8.0",
+  "version": "3.8.1",
   "description": "Experience the fast and beautiful anti-aliased rendering of WebGL/WebGPU. You can create rich, interactive graphics, cross-platform applications and games without worrying about browser or device compatibility.",
   "author": "Toshiyuki Ienaga<ienaga@next2d.app> (https://github.com/ienaga/)",
   "license": "MIT",
diff --git a/packages/text/src/TextArea/service/TextAreaMovePositionService.test.ts b/packages/text/src/TextArea/service/TextAreaMovePositionService.test.ts
index fd07d427..4334cbec 100644
--- a/packages/text/src/TextArea/service/TextAreaMovePositionService.test.ts
+++ b/packages/text/src/TextArea/service/TextAreaMovePositionService.test.ts
@@ -1,31 +1,87 @@
 import type { TextField } from "../../TextField";
 import { execute } from "./TextAreaMovePositionService";
 import { describe, expect, it } from "vitest";
-import {
-    $textArea,
-} from "../../TextUtil";
+import { $textArea } from "../../TextUtil";
+
+/**
+ * テスト環境では stage.rendererScale = 1 / rendererWidth = stageWidth = 0 /
+ * $mainCanvasPosition = (0, 0) / devicePixelRatio = 1 のため、
+ * localToGlobal を恒等変換にすると textarea の left/top はカーソルのローカル座標と一致する。
+ */
+const createTextField = (override: Partial<TextField>): TextField =>
+{
+    return {
+        "localToGlobal": (point: { x: number; y: number }) => ({ "x": point.x, "y": point.y }),
+        "scrollX": 0,
+        "scrollY": 0,
+        ...override
+    } as unknown as TextField;
+};
 
 describe("TextAreaMovePositionService.js Test", () =>
 {
-    it("test case", () =>
+    it("カーソルが行の途中にある場合、カーソルのx位置・行の上端(真裏)に配置され、高さがテキストサイズに合う", () =>
     {
-        // Arrange
-        const textField = {
-            localToGlobal: () => ({ x: 20, y: 30 }),
-            $textData: {
-                textTable: [
-                    { line: 0, mode: "break", w: 10 },
-                    { line: 1, mode: "normal", w: 20 },
+        // 1行目「あい」、focusIndex=2（「い」の前）、フォントサイズ20
+        const textField = createTextField({
+            "focusIndex": 2,
+            "$textData": {
+                "textTable": [
+                    { "line": 0, "mode": "break", "w": 0 },
+                    { "line": 0, "mode": "text", "w": 24, "textFormat": { "size": 20 } },
+                    { "line": 0, "mode": "text", "w": 24, "textFormat": { "size": 20 } }
                 ],
-                heightTable: [10, 20],
+                "heightTable": [24]
+            }
+        } as unknown as TextField);
+
+        execute(textField);
+
+        // x = 「あ」の幅(24)、y = 1行目の上端(0)
+        expect($textArea.style.left).toBe("24px");
+        expect($textArea.style.top).toBe("0px");
+        // 高さ = 行高(24)、font-size = テキストサイズ(20)（テスト環境では scale=1）
+        expect($textArea.style.height).toBe("24px");
+        expect($textArea.style.fontSize).toBe("20px");
+    });
+
+    it("カーソルが文末(textTable[focusIndex]が未定義)にある場合でも、最後の文字の行・末尾に配置される", () =>
+    {
+        // 「あいうえお\nかきくけこ」、focusIndex=12（文末）
+        const textTable = [{ "line": 0, "mode": "break", "w": 0 }];
+        for (let idx = 0; idx < 5; idx++) {
+            textTable.push({ "line": 0, "mode": "text", "w": 24 });
+        }
+        textTable.push({ "line": 1, "mode": "break", "w": 0 });
+        for (let idx = 0; idx < 5; idx++) {
+            textTable.push({ "line": 1, "mode": "text", "w": 24 });
+        }
+
+        const textField = createTextField({
+            "focusIndex": textTable.length, // 12 = 文末
+            "$textData": {
+                textTable,
+                "heightTable": [24, 24]
             }
-        } as unknown as TextField;
+        } as unknown as TextField);
+
+        execute(textField);
+
+        // x = 2行目「かきくけこ」の幅(120)、y = 2行目の上端(24)
+        expect($textArea.style.left).toBe("120px");
+        expect($textArea.style.top).toBe("24px");
+    });
+
+    it("$textData が無い場合は原点(0,0)に配置される", () =>
+    {
+        const textField = createTextField({
+            "focusIndex": 1,
+            "$textData": null
+        } as unknown as TextField);
 
-        // Act
         execute(textField);
 
-        // Assert
-        expect($textArea.style.left).toBe("20px");
-        expect($textArea.style.top).toBe("30px");
+        expect($textArea.style.left).toBe("0px");
+        expect($textArea.style.top).toBe("0px");
     });
-});
\ No newline at end of file
+});
diff --git a/packages/text/src/TextArea/service/TextAreaMovePositionService.ts b/packages/text/src/TextArea/service/TextAreaMovePositionService.ts
index 6f0e985c..8dce7846 100644
--- a/packages/text/src/TextArea/service/TextAreaMovePositionService.ts
+++ b/packages/text/src/TextArea/service/TextAreaMovePositionService.ts
@@ -12,9 +12,107 @@ import {
  */
 const $devicePixelRatio: number = window.devicePixelRatio;
 
+/**
+ * @description フォーカスしているテキストのカーソル位置（ローカル座標）を算出します。
+ *              入力中の文字の「真裏」に input(textarea) を配置するため、カーソルのある行の
+ *              上端を基準に x/y を返却します。これにより IME の変換文字が canvas 側の文字に
+ *              ちょうど重なり、他の文字に被らないようにします。カーソルが文末にある場合
+ *              (textTable[focusIndex] が存在しない場合)も直前の文字から行と x を求めます。
+ *              Calculate the caret position (local coordinates) of the focused text.
+ *              Returns x/y based on the top of the caret line so that the input(textarea)
+ *              is placed directly behind the character being typed, making the IME
+ *              composition overlap the canvas character (and not other characters).
+ *              Handles the end-of-text case (textTable[focusIndex] is undefined) by using
+ *              the previous character.
+ *
+ *              あわせて、input(textarea) の高さ・フォントサイズを canvas のテキストサイズへ
+ *              合わせるため、カーソル行の行高(lineHeight)とフォントサイズ(fontSize)も返却します。
+ *              Also returns the caret line height and font size so that the input(textarea)
+ *              height/font-size can match the canvas text size.
+ *
+ * @param  {TextField} text_field
+ * @return {{ x: number, y: number, lineHeight: number, fontSize: number }}
+ * @method
+ * @private
+ */
+const calcCaretLocalPosition = (
+    text_field: TextField
+): { x: number; y: number; lineHeight: number; fontSize: number } =>
+{
+    const textData = text_field.$textData;
+    if (!textData) {
+        return { "x": 0, "y": 0, "lineHeight": 0, "fontSize": 0 };
+    }
+
+    const textTable = textData.textTable;
+
+    // カーソル行の決定
+    let caretLine = 0;
+    const focusIndex = text_field.focusIndex;
+    const focusTextObject = textTable[focusIndex];
+    if (focusTextObject) {
+        // 改行・折り返しの直前にカーソルがある場合は前の行の末尾を指す
+        caretLine = focusTextObject.mode === "break" || focusTextObject.mode === "wrap"
+            ? focusTextObject.line - 1
+            : focusTextObject.line;
+    } else {
+        // 文末（textTable[focusIndex] が存在しない）は直前の文字の行を採用
+        const lastTextObject = textTable[textTable.length - 1];
+        caretLine = lastTextObject ? lastTextObject.line : 0;
+    }
+
+    if (caretLine < 0) {
+        caretLine = 0;
+    }
+
+    // カーソル行で、カーソルより前にある文字幅の合計（= カーソルの x 位置）
+    let x = 0;
+    for (let idx = 1; idx < textTable.length; ++idx) {
+        if (idx >= focusIndex) {
+            break;
+        }
+        const textObject = textTable[idx];
+        if (!textObject || textObject.mode !== "text" || textObject.line !== caretLine) {
+            continue;
+        }
+        x += textObject.w;
+    }
+
+    // カーソル行の上端（= 入力文字の真裏）
+    let y = 0;
+    for (let idx = 0; idx < caretLine; ++idx) {
+        y += textData.heightTable[idx] || 0;
+    }
+
+    // カーソル行の行高（= input の高さに使用）
+    const lineHeight = textData.heightTable[caretLine] || 0;
+
+    // カーソル行のフォントサイズ（= input の font-size に使用）。
+    // カーソル位置までの最後の文字サイズを優先し、無ければ defaultTextFormat を採用する。
+    let fontSize = text_field.defaultTextFormat?.size || 0;
+    for (let idx = 1; idx < textTable.length; ++idx) {
+        const textObject = textTable[idx];
+        if (!textObject || textObject.mode !== "text" || textObject.line !== caretLine) {
+            continue;
+        }
+        if (textObject.textFormat?.size) {
+            fontSize = textObject.textFormat.size;
+        }
+        if (idx >= focusIndex) {
+            break;
+        }
+    }
+
+    return { x, y, lineHeight, fontSize };
+};
+
 /**
  * @description フォーカスしているテキストの位置にテキストエリアを移動します。
+ *              入力中の文字の真裏に input(textarea) を配置し、高さ・フォントサイズを
+ *              canvas のテキストサイズに合わせます。
  *              Move the text area to the position of the text that is focusing.
+ *              The input(textarea) is placed directly behind the character being typed,
+ *              and its height/font-size are matched to the canvas text size.
  *
  * @param  {TextField} text_field
  * @return {void}
@@ -23,32 +121,39 @@ const $devicePixelRatio: number = window.devicePixelRatio;
  */
 export const execute = (text_field: TextField): void =>
 {
-    const point = text_field.localToGlobal(new Point());
+    const caret = calcCaretLocalPosition(text_field);
 
-    const textData = text_field.$textData;
-    if (textData) {
-
-        const focusTextObject = textData.textTable[text_field.focusIndex];
-        if (focusTextObject) {
-            for (let idx = text_field.focusIndex - 1; idx > -1; --idx) {
-                const textObject = textData.textTable[idx];
-                if (!textObject || textObject.line !== focusTextObject.line) {
-                    break;
-                }
-                point.x += textObject.w;
-            }
-
-            const line = focusTextObject.mode === "break"
-                ? focusTextObject.line - 1
-                : focusTextObject.line;
-
-            for (let idx = 0; idx < line; ++idx) {
-                point.y += textData.heightTable[idx];
-            }
-        }
+    // スクロール量を反映して、表示されているカーソル位置に補正する
+    let localX = caret.x;
+    if (text_field.scrollX > 0) {
+        const width = text_field.width;
+        localX -= text_field.scrollX * (text_field.textWidth - width) / width;
+    }
+
+    let localY = caret.y;
+    if (text_field.scrollY > 0) {
+        const height = text_field.height;
+        localY -= text_field.scrollY * (text_field.textHeight - height) / height;
     }
 
+    // ローカル座標をステージ座標へ変換（TextField のスケール・回転・配置を考慮）
+    const point = text_field.localToGlobal(new Point(localX, localY));
+
+    // ステージ座標 → 画面(CSS)座標へ変換。
+    // PlayerSetCurrentMousePointService の逆変換に対応する。
     const scale = stage.rendererScale / $devicePixelRatio;
-    $textArea.style.left = `${$mainCanvasPosition.x + point.x * scale}px`;
-    $textArea.style.top  = `${$mainCanvasPosition.y + point.y * scale}px`;
-};
\ No newline at end of file
+    const tx = (stage.rendererWidth  - stage.stageWidth  * stage.rendererScale) / 2;
+    const ty = (stage.rendererHeight - stage.stageHeight * stage.rendererScale) / 2;
+
+    $textArea.style.left = `${$mainCanvasPosition.x + tx / $devicePixelRatio + point.x * scale}px`;
+    $textArea.style.top  = `${$mainCanvasPosition.y + ty / $devicePixelRatio + point.y * scale}px`;
+
+    // canvas のテキストサイズに合わせて input の高さ・フォントサイズを設定する
+    const lineHeight = caret.lineHeight;
+    if (lineHeight > 0) {
+        const fontSize = caret.fontSize || lineHeight;
+        $textArea.style.height   = `${lineHeight * scale}px`;
+        $textArea.style.fontSize = `${fontSize * scale}px`;
+        $textArea.style.lineHeight = `${lineHeight * scale}px`;
+    }
+};
diff --git a/src/index.ts b/src/index.ts
index 0bf27f51..bb6b72fe 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,7 +3,7 @@
 import { Next2D } from "@next2d/core";
 
 if (!("next2d" in window)) {
-    console.log("%c Next2D Player %c 3.8.0 %c https://next2d.app",
+    console.log("%c Next2D Player %c 3.8.1 %c https://next2d.app",
         "color: #fff; background: #5f5f5f",
         "color: #fff; background: #4bc729",
         "");