diff --git a/src/backend/browser/fileImpl.ts b/src/backend/browser/fileImpl.ts
index 25c3f6684c..d60f85f30f 100644
--- a/src/backend/browser/fileImpl.ts
+++ b/src/backend/browser/fileImpl.ts
@@ -3,6 +3,9 @@ import { directoryHandleStoreKey } from "./contract";
 import { openDB } from "./browserConfig";
 import { SandboxKey } from "@/type/preload";
 import { failure, success } from "@/type/result";
+import { createLogger } from "@/domain/frontend/log";
+
+const log = createLogger("fileImpl");
 
 const storeDirectoryHandle = async (
   directoryHandle: FileSystemDirectoryHandle,
@@ -176,3 +179,45 @@ export const checkFileExistsImpl: (typeof window)[typeof SandboxKey]["checkFileE
 
     return Promise.resolve(fileEntries.includes(fileName));
   };
+
+// FileSystemFileHandleを保持するMap。キーは生成した疑似パス。
+const fileHandleMap: Map<string, FileSystemFileHandle> = new Map();
+
+// ファイル選択ダイアログを開く
+// 返り値はファイルパスではなく、疑似パスを返す
+export const showOpenFilePickerImpl = async (options: {
+  multiple: boolean;
+  fileTypes: {
+    description: string;
+    accept: Record<string, string[]>;
+  }[];
+}) => {
+  try {
+    const handles = await showOpenFilePicker({
+      excludeAcceptAllOption: true,
+      multiple: options.multiple,
+      types: options.fileTypes,
+    });
+    const paths = [];
+    for (const handle of handles) {
+      const fakePath = `<browser-dummy-${crypto.randomUUID()}>-${handle.name}`;
+      fileHandleMap.set(fakePath, handle);
+      paths.push(fakePath);
+    }
+    return handles.length > 0 ? paths : undefined;
+  } catch (e) {
+    log.warn(`showOpenFilePicker error: ${e}`);
+    return undefined;
+  }
+};
+
+// 指定した疑似パスのファイルを読み込む
+export const readFileImpl = async (filePath: string) => {
+  const fileHandle = fileHandleMap.get(filePath);
+  if (fileHandle == undefined) {
+    return failure(new Error(`ファイルが見つかりません: ${filePath}`));
+  }
+  const file = await fileHandle.getFile();
+  const buffer = await file.arrayBuffer();
+  return success(buffer);
+};
diff --git a/src/backend/browser/sandbox.ts b/src/backend/browser/sandbox.ts
index f3e298054d..f2f5451085 100644
--- a/src/backend/browser/sandbox.ts
+++ b/src/backend/browser/sandbox.ts
@@ -1,7 +1,9 @@
 import { defaultEngine } from "./contract";
 import {
   checkFileExistsImpl,
+  readFileImpl,
   showOpenDirectoryDialogImpl,
+  showOpenFilePickerImpl,
   writeFileImpl,
 } from "./fileImpl";
 import { getConfigManager } from "./browserConfig";
@@ -127,10 +129,18 @@ export const api: Sandbox = {
       }
     });
   },
-  showProjectLoadDialog(/* obj: { title: string } */) {
-    throw new Error(
-      "ブラウザ版では現在ファイルの読み込みをサポートしていません",
-    );
+  async showProjectLoadDialog() {
+    return showOpenFilePickerImpl({
+      multiple: false,
+      fileTypes: [
+        {
+          description: "Voicevox Project File",
+          accept: {
+            "application/json": [".vvproj"],
+          },
+        },
+      ],
+    });
   },
   showMessageDialog(obj: {
     type: "none" | "info" | "error" | "question" | "warning";
@@ -156,18 +166,35 @@ export const api: Sandbox = {
       `Not implemented: showQuestionDialog, request: ${JSON.stringify(obj)}`,
     );
   },
-  showImportFileDialog(/* obj: { title: string } */) {
-    throw new Error(
-      "ブラウザ版では現在ファイルの読み込みをサポートしていません",
-    );
+  async showImportFileDialog(obj: {
+    name?: string;
+    extensions?: string[];
+    title: string;
+  }) {
+    const fileHandle = await showOpenFilePickerImpl({
+      multiple: false,
+      fileTypes: [
+        {
+          description: obj.name ?? "Text",
+          accept: obj.extensions
+            ? {
+                "application/octet-stream": obj.extensions.map(
+                  (ext) => `.${ext}`,
+                ),
+              }
+            : {
+                "plain/text": [".txt"],
+              },
+        },
+      ],
+    });
+    return fileHandle?.[0];
   },
   writeFile(obj: { filePath: string; buffer: ArrayBuffer }) {
     return writeFileImpl(obj);
   },
-  readFile(/* obj: { filePath: string } */) {
-    throw new Error(
-      "ブラウザ版では現在ファイルの読み込みをサポートしていません",
-    );
+  readFile(obj: { filePath: string }) {
+    return readFileImpl(obj.filePath);
   },
   isAvailableGPUMode() {
     // TODO: WebAssembly版をサポートする時に実装する
diff --git a/src/type/preload.ts b/src/type/preload.ts
index 67b32c34cb..01a3bdecb7 100644
--- a/src/type/preload.ts
+++ b/src/type/preload.ts
@@ -7,25 +7,28 @@ export const isProduction = import.meta.env.MODE === "production";
 export const isElectron = import.meta.env.VITE_TARGET === "electron";
 export const isBrowser = import.meta.env.VITE_TARGET === "browser";
 
-// electronのメイン・レンダラープロセス内、ブラウザ内どこでも使用可能なmacOS判定
-function checkIsMac(): boolean {
-  let isMac: boolean | undefined = undefined;
+// electronのメイン・レンダラープロセス内、ブラウザ内どこでも使用可能なOS判定
+function checkOs(os: "windows" | "mac"): boolean {
+  let isSpecifiedOs: boolean | undefined = undefined;
   if (process?.platform) {
     // electronのメインプロセス用
-    isMac = process.platform === "darwin";
+    isSpecifiedOs =
+      process.platform === (os === "windows" ? "win32" : "darwin");
   } else if (navigator?.userAgentData) {
     // electronのレンダラープロセス用、Chrome系統が実装する実験的機能
-    isMac = navigator.userAgentData.platform.toLowerCase().includes("mac");
+    isSpecifiedOs = navigator.userAgentData.platform.toLowerCase().includes(os);
   } else if (navigator?.platform) {
     // ブラウザ用、非推奨機能
-    isMac = navigator.platform.toLowerCase().includes("mac");
+    isSpecifiedOs = navigator.platform.toLowerCase().includes(os);
   } else {
     // ブラウザ用、不正確
-    isMac = navigator.userAgent.toLowerCase().includes("mac");
+    isSpecifiedOs = navigator.userAgent.toLowerCase().includes(os);
   }
-  return isMac;
+  return isSpecifiedOs;
 }
-export const isMac = checkIsMac();
+
+export const isMac = checkOs("mac");
+export const isWindows = checkOs("windows");
 
 const urlStringSchema = z.string().url().brand("URL");
 export type UrlString = z.infer<typeof urlStringSchema>;