The currency in Japan is the Yen. The note pictured is the 1000 Yen bill which is the smallest. The other notes are 5000 and 10000 yen. Just recently a 2000 Yen note was introduced in Japan. The coins come in 500,100,50,10,5 and 1 yen denominations.
When travelling to Japan the best thing to do is to change your money into Yen cash (or if you are coming from the US then American Dollars is fine) as Japan is a cash based society. It is very common to walk around with the equivalent of $500US in cash or more!
The debit card and credit card craze of most societies has never caught on in Japan. Most foreign credit cards are not accepted in shops, restaurants and even some hotels. It is possible to get a cash advance from a Visa card at some ATM machines or banks but don't count on it! In Nagano the best place to go to get cash advances from your visa card is the ATM on the ground floor of the Heiando book store building opposite Nagano Station.
To find out how much the Yen is worth take a look at this currency converter