There is no limit on the amount of any currency that may be brought into or taken out of Japan. However, if you transport (any currencies, checks, securities or other monies) exceeding 1,000,000 yen worth in Japanese currency into or out of the country then you must complete a customs declaration.
The unit of Japanese currency is yen. Coins are available in denominations of 1, 5, 10, 50, 100 and 500 yen and bank notes in denominations of 1,000, 2,000, 5,000 and 10,000 yen.
You can buy yen at foreign exchange banks and other authorized money exchangers. At the international airports, currency exchange counters are usually open during normal office hours. The exchange rate fluctuates daily depending on the money market.