The yen is the unit of currency in Japan. There are four kinds of bills (10,000 yen, 5,000 yen, 2,000 yen, 1,000 yen) and six kinds of coins (500 yen, 100 yen, 50 yen, 10 yen, 5 yen, 1 yen) used. All of the bills and coins are different sizes. For example, the bills descend in size from 10,000 Yen to 1,000 Yen. For more information about the yen bills and coins, please visit websites of Japan Mint and National Printing Bureau.
Traveler's checks and some foreign currencies can be used as a means of payment at most large hotels and duty-free shops. However, most of businesses do not accept currency other than Japanese yen. You might want to exchange your money before you leave the airport. You can also exchange your money into yen at authorized foreign exchange banks in Japan.