diff --git a/src/backend/electron/manager/engineInfoManager.ts b/src/backend/electron/manager/engineInfoManager.ts
index 83308f0844..17a41a0ff3 100644
--- a/src/backend/electron/manager/engineInfoManager.ts
+++ b/src/backend/electron/manager/engineInfoManager.ts
@@ -15,35 +15,11 @@ import {
   minimumEngineManifestSchema,
 } from "@/type/preload";
 import { AltPortInfos } from "@/store/type";
+import { UnreachableError } from "@/type/utility";
 import { loadEnvEngineInfos } from "@/domain/defaultEngine/envEngineInfo";
+import { failure, Result, success } from "@/type/result";
 
-/**
- * デフォルトエンジンの情報を取得する
- */
-function fetchDefaultEngineInfos(defaultEngineDir: string): EngineInfo[] {
-  // TODO: envから直接ではなく、envに書いたengine_manifest.jsonから情報を得るようにする
-  const engines = loadEnvEngineInfos();
-
-  return engines.map((engineInfo) => {
-    const { protocol, hostname, port, pathname } = new URL(engineInfo.host);
-    return {
-      ...engineInfo,
-      protocol,
-      hostname,
-      defaultPort: port,
-      pathname: pathname === "/" ? "" : pathname,
-      isDefault: true,
-      type: "path",
-      executionFilePath: path.resolve(engineInfo.executionFilePath),
-      path:
-        engineInfo.path == undefined
-          ? undefined
-          : path.resolve(defaultEngineDir, engineInfo.path),
-    } satisfies EngineInfo;
-  });
-}
-
-/** エンジンの情報を管理するクラス */
+/** 利用可能なエンジンの情報を管理するクラス */
 export class EngineInfoManager {
   defaultEngineDir: string;
   vvppEngineDir: string;
@@ -51,49 +27,91 @@ export class EngineInfoManager {
   /** 代替ポート情報 */
   public altPortInfos: AltPortInfos = {};
 
+  private envEngineInfos = loadEnvEngineInfos();
+
   constructor(payload: { defaultEngineDir: string; vvppEngineDir: string }) {
     this.defaultEngineDir = payload.defaultEngineDir;
     this.vvppEngineDir = payload.vvppEngineDir;
   }
 
+  /** デフォルトエンジンかどうかを判定する */
+  private isDefaultEngine(engineId: EngineId): boolean {
+    return this.envEngineInfos.some((e) => e.uuid === engineId);
+  }
+
+  /** エンジンディレクトリからエンジン情報を読み込む */
+  private loadEngineInfo(
+    engineDir: string,
+    type: "vvpp" | "path",
+  ): Result<EngineInfo, "manifestNotFound" | "manifestParseError"> {
+    const manifestPath = path.join(engineDir, "engine_manifest.json");
+    if (!fs.existsSync(manifestPath)) {
+      return failure("manifestNotFound", new Error("manifest not found"));
+    }
+    let manifest: MinimumEngineManifestType;
+    try {
+      manifest = minimumEngineManifestSchema.parse(
+        JSON.parse(fs.readFileSync(manifestPath, { encoding: "utf8" })),
+      );
+    } catch (e) {
+      if (e instanceof Error) {
+        return failure("manifestParseError", e);
+      } else {
+        throw new UnreachableError();
+      }
+    }
+
+    const [command, ...args] = shlex.split(manifest.command);
+
+    const engineInfo = {
+      uuid: manifest.uuid,
+      protocol: "http:",
+      hostname: "127.0.0.1",
+      defaultPort: manifest.port.toString(),
+      pathname: "",
+      name: manifest.name,
+      path: engineDir,
+      executionEnabled: true,
+      executionFilePath: path.join(engineDir, command),
+      executionArgs: args,
+      type,
+      isDefault: this.isDefaultEngine(manifest.uuid),
+    } satisfies EngineInfo;
+    return success(engineInfo);
+  }
+
   /**
-   * 追加エンジンの一覧を取得する。
-   * FIXME: store.get("registeredEngineDirs")への副作用をEngineManager外に移動する
+   * .envにあるエンジンの情報を取得する。
+   * ダウンロードが必要なものは除外されている。
    */
-  private fetchAdditionalEngineInfos(): EngineInfo[] {
-    const engines: EngineInfo[] = [];
-    const addEngine = (engineDir: string, type: "vvpp" | "path") => {
-      const manifestPath = path.join(engineDir, "engine_manifest.json");
-      if (!fs.existsSync(manifestPath)) {
-        return "manifestNotFound";
-      }
-      let manifest: MinimumEngineManifestType;
-      try {
-        manifest = minimumEngineManifestSchema.parse(
-          JSON.parse(fs.readFileSync(manifestPath, { encoding: "utf8" })),
-        );
-      } catch (e) {
-        return "manifestParseError";
-      }
+  private fetchEnvEngineInfos(): EngineInfo[] {
+    // TODO: envから直接ではなく、envに書いたengine_manifest.jsonから情報を得るようにする
+    const engines = loadEnvEngineInfos();
+
+    return engines.map((engineInfo) => {
+      const { protocol, hostname, port, pathname } = new URL(engineInfo.host);
+      return {
+        ...engineInfo,
+        protocol,
+        hostname,
+        defaultPort: port,
+        pathname: pathname === "/" ? "" : pathname,
+        isDefault: true,
+        type: "path",
+        executionFilePath: path.resolve(engineInfo.executionFilePath),
+        path:
+          engineInfo.path == undefined
+            ? undefined
+            : path.resolve(this.defaultEngineDir, engineInfo.path),
+      } satisfies EngineInfo;
+    });
+  }
 
-      const [command, ...args] = shlex.split(manifest.command);
-
-      engines.push({
-        uuid: manifest.uuid,
-        protocol: "http:",
-        hostname: "127.0.0.1",
-        defaultPort: manifest.port.toString(),
-        pathname: "",
-        name: manifest.name,
-        path: engineDir,
-        executionEnabled: true,
-        executionFilePath: path.join(engineDir, command),
-        executionArgs: args,
-        type,
-        isDefault: false,
-      } satisfies EngineInfo);
-      return "ok";
-    };
+  /**
+   * VVPPエンジン情報の一覧を取得する。
+   */
+  private fetchVvppEngineInfos(): EngineInfo[] {
+    const engineInfos: EngineInfo[] = [];
     for (const dirName of fs.readdirSync(this.vvppEngineDir)) {
       const engineDir = path.join(this.vvppEngineDir, dirName);
       if (!fs.statSync(engineDir).isDirectory()) {
@@ -103,17 +121,28 @@ export class EngineInfoManager {
       if (dirName === ".tmp") {
         continue;
       }
-      const result = addEngine(engineDir, "vvpp");
-      if (result !== "ok") {
-        log.log(`Failed to load engine: ${result}, ${engineDir}`);
+      const result = this.loadEngineInfo(engineDir, "vvpp");
+      if (!result.ok) {
+        log.log(`Failed to load engine: ${result.code}, ${engineDir}`);
+        continue;
       }
+      engineInfos.push(result.value);
     }
+    return engineInfos;
+  }
+
+  /**
+   * 設定で登録したエンジン情報を取得する。
+   * FIXME: store.get("registeredEngineDirs")への副作用をEngineManager外に移動する
+   */
+  private fetchRegisteredEngineInfos(): EngineInfo[] {
     const configManager = getConfigManager();
-    // FIXME: この関数の引数でregisteredEngineDirsを受け取り、動かないエンジンをreturnして、EngineManager外でconfig.setする
+
+    const engineInfos: EngineInfo[] = [];
     for (const engineDir of configManager.get("registeredEngineDirs")) {
-      const result = addEngine(engineDir, "path");
-      if (result !== "ok") {
-        log.log(`Failed to load engine: ${result}, ${engineDir}`);
+      const result = this.loadEngineInfo(engineDir, "path");
+      if (!result.ok) {
+        log.log(`Failed to load engine: ${result.code}, ${engineDir}`);
         // 動かないエンジンは追加できないので削除
         // FIXME: エンジン管理UIで削除可能にする
         dialog.showErrorBox(
@@ -126,18 +155,21 @@ export class EngineInfoManager {
             .get("registeredEngineDirs")
             .filter((p) => p !== engineDir),
         );
+        continue;
       }
+      engineInfos.push(result.value);
     }
-    return engines;
+    return engineInfos;
   }
 
   /**
-   * 全てのエンジンの一覧を取得する。デフォルトエンジン＋追加エンジン。
+   * 全てのエンジンの一覧を取得する。
    */
   fetchEngineInfos(): EngineInfo[] {
     const engineInfos = [
-      ...fetchDefaultEngineInfos(this.defaultEngineDir),
-      ...this.fetchAdditionalEngineInfos(),
+      ...this.fetchEnvEngineInfos(),
+      ...this.fetchVvppEngineInfos(),
+      ...this.fetchRegisteredEngineInfos(),
     ];
     return engineInfos;
   }