Cards are generally accepted at major department stores and in upmarket restaurants. However Japan remains very much a cash-based society and you will have trouble using your cards in smaller shops and restaurants.
We encourage our customers to carry cash with them and not to rely on cards for making purchases. You can use your cards to withdraw Japanese Yen from ATMs (cash machines) at all post offices in Japan (large and small) and at 7-Eleven convenience stores.
You will need your 4-digit PIN code to make withdrawals and it is a good idea to let your bank at home know in advance that you will be using your card in Japan. ATMs have instructions in English so you won't have any problems - just make sure you get the 0s right!