The Japan currency is yen (JPY). They have 4 type of bills - 1000 yen, 2000 yen, 5000 yen, 10000 yen, and 6 types of coins - 1 yen, 5 yen, 10 yen, 50 yen, 100 yen, 500 yen.
You should keep in mind that Japan is still cash culture and there are still a lot of restaurants or shops which not accept credit card. Foreign currencies are generally not accepted in Japan also. So you should always carry cash on your trip. You can exchange to Japanese Yen at airport or withdraw at ATM like in convinience stores.
Please check here for exchange rate of other currencies with Japanese Yen
Collected from FreeCurrencyRates.com