Credit, debit and prepaid cards of international brands are generally accepted throughout the country. There will be instances where stores may not display the symbols of the cards they accept, so ask the salesperson if you can use your card. You can use cards to pay for Narita Express (JR) and shinkansen (JR) fares, however, you can't always use them for short distance train/subway fares. You can withdraw cash nationwide at ATMs in Japan Post Bank and in Seven Bank. Research into using credits cards in Japan is recommended.
If you should lose your credit card contact the issuers directly to arrange for replacements. We recommend that you keep a list of toll free numbers for the issuer, and separate them from your cards.
If you are uncomfortable carrying a large amount of cash with you, another option is to purchase a Suica card or Pasmo card . These cards aren't simply for using the trains—you can use them on many other forms of public transport, as well as at convenience stores, and an increasing number of shops and restaurants. While they can't be used everywhere, they can be a useful alternative to carrying cash.