For foreign currencies, there is no limit on the amount you can bring into Japan, but amounts exceeding 1 million yen equivalent in foreign currencies must also be declared to customs.
It's important to note that these regulations apply to cash only. Other valuable items such as jewelry, precious metals, and antiques may have different regulations and may need to be declared to customs separately.
For more detailed and up-to-date information, it's always a good idea to consult the latest regulations from the Japan Customs website or contact the Japanese Embassy or Consulate in your country before your trip.