diff --git a/packages/core/src/locales.ts b/packages/core/src/locales.ts
index 5e0ed62a75..b7180c3400 100644
--- a/packages/core/src/locales.ts
+++ b/packages/core/src/locales.ts
@@ -1,5 +1,6 @@
 import az from "./locales/az.js";
 import en from "./locales/en.js";
 import es from "./locales/es.js";
+import ja from "./locales/ja.js";
 
-export { az, es, en };
+export { az, es, en, ja };
diff --git a/packages/core/src/locales/ja.ts b/packages/core/src/locales/ja.ts
new file mode 100644
index 0000000000..ff1ad5f8ef
--- /dev/null
+++ b/packages/core/src/locales/ja.ts
@@ -0,0 +1,122 @@
+import type { $ZodStringFormats } from "../checks.js";
+import type * as errors from "../errors.js";
+import * as util from "../util.js";
+
+const Sizable: Record<string, { unit: string; verb: string }> = {
+  string: { unit: "文字", verb: "である" },
+  file: { unit: "バイト", verb: "である" },
+  array: { unit: "要素", verb: "である" },
+  set: { unit: "要素", verb: "である" },
+};
+
+function getSizing(origin: string): { unit: string; verb: string } | null {
+  return Sizable[origin] ?? null;
+}
+
+export const parsedType = (data: any): string => {
+  const t = typeof data;
+
+  switch (t) {
+    case "number": {
+      return Number.isNaN(data) ? "NaN" : "数値";
+    }
+    case "object": {
+      if (Array.isArray(data)) {
+        return "配列";
+      }
+      if (data === null) {
+        return "null";
+      }
+
+      if (Object.getPrototypeOf(data) !== Object.prototype && data.constructor) {
+        return data.constructor.name;
+      }
+    }
+  }
+  return t;
+};
+
+const Nouns: {
+  [k in $ZodStringFormats | (string & {})]?: string;
+} = {
+  regex: "入力値",
+  email: "メールアドレス",
+  url: "URL",
+  emoji: "絵文字",
+  uuid: "UUID",
+  uuidv4: "UUIDv4",
+  uuidv6: "UUIDv6",
+  nanoid: "nanoid",
+  guid: "GUID",
+  cuid: "cuid",
+  cuid2: "cuid2",
+  ulid: "ULID",
+  xid: "XID",
+  ksuid: "KSUID",
+  datetime: "ISO日時",
+  date: "ISO日付",
+  time: "ISO時刻",
+  duration: "ISO期間",
+  ipv4: "IPv4アドレス",
+  ipv6: "IPv6アドレス",
+  cidrv4: "IPv4範囲",
+  cidrv6: "IPv6範囲",
+  base64: "base64エンコード文字列",
+  base64url: "base64urlエンコード文字列",
+  json_string: "JSON文字列",
+  e164: "E.164番号",
+  jwt: "JWT",
+  template_literal: "入力値",
+};
+
+const error: errors.$ZodErrorMap = (issue) => {
+  switch (issue.code) {
+    case "invalid_type":
+      return `無効な入力: ${issue.expected}が期待されましたが、${parsedType(issue.input)}が入力されました`;
+    case "invalid_value":
+      if (issue.values.length === 1) return `無効な入力: ${util.stringifyPrimitive(issue.values[0])}が期待されました`;
+      return `無効な選択: ${util.joinValues(issue.values, "、")}のいずれかである必要があります`;
+    case "too_big": {
+      const adj = issue.inclusive ? "<=" : "<";
+      const sizing = getSizing(issue.origin);
+      if (sizing)
+        return `大きすぎる値: ${issue.origin ?? "値"}は${issue.maximum.toString()}${sizing.unit ?? "要素"}${adj}である必要があります`;
+      return `大きすぎる値: ${issue.origin ?? "値"}は${issue.maximum.toString()}${adj}である必要があります`;
+    }
+    case "too_small": {
+      const adj = issue.inclusive ? ">=" : ">";
+      const sizing = getSizing(issue.origin);
+      if (sizing)
+        return `小さすぎる値: ${issue.origin}は${issue.minimum.toString()}${sizing.unit}${adj}である必要があります`;
+      return `小さすぎる値: ${issue.origin}は${issue.minimum.toString()}${adj}である必要があります`;
+    }
+    case "invalid_format": {
+      const _issue = issue as errors.$ZodStringFormatIssues;
+      if (_issue.format === "starts_with") return `無効な文字列: "${issue}"で始まる必要があります`;
+      if (_issue.format === "ends_with") return `無効な文字列: "${_issue.suffix}"で終わる必要があります`;
+      if (_issue.format === "includes") return `無効な文字列: "${_issue.includes}"を含む必要があります`;
+      if (_issue.format === "regex") return `無効な文字列: パターン${_issue.pattern}に一致する必要があります`;
+      return `無効な${Nouns[_issue.format] ?? issue.format}`;
+    }
+    case "not_multiple_of":
+      return `無効な数値: ${issue.divisor}の倍数である必要があります`;
+    case "unrecognized_keys":
+      return `認識されていないキー${issue.keys.length > 1 ? "群" : ""}: ${util.joinValues(issue.keys, "、")}`;
+    case "invalid_key":
+      return `${issue.origin}内の無効なキー`;
+    case "invalid_union":
+      return "無効な入力";
+    case "invalid_element":
+      return `${issue.origin}内の無効な値`;
+    default:
+      return `無効な入力`;
+  }
+};
+
+export { error };
+
+export default function (): { localeError: errors.$ZodErrorMap } {
+  return {
+    localeError: error,
+  };
+}
diff --git a/packages/docs/content/error-customization.mdx b/packages/docs/content/error-customization.mdx
index 5795950067..8125c1218e 100644
--- a/packages/docs/content/error-customization.mdx
+++ b/packages/docs/content/error-customization.mdx
@@ -357,6 +357,7 @@ The following locales are available:
 
 - `az` — Azerbaijani
 - `en` — English
+- `ja` — Japanese 
 
 ## Error precedence
 
@@ -389,4 +390,3 @@ Below is a quick reference for determining error precedence: if multiple error c
   ```ts
   z.config(z.locales.en());
   ```
-