Japan is a cash society. Visitors are advised to carry sufficient cash with them when travelling around. The cash you carry around should be enough to cover any travel expenses, accommodation fees, meals and entrance fees for attractions.
You may bring Japanese yen from your country and there is no upper limit on the amount you are allowed to bring into Japan. If the amount exceeds 1,000,000 yen, you must complete a customs declaration. This is also the case if you carry more than this amount when leaving Japan.
Notes come in 1,000 yen, 2,000 yen, 5,000 yen and 10,000 denominations. Coins for 1 yen, 5 yen, 10 yen, 50 yen, 100 yen and 500 yen are used. In most shops and facilities you can pay with large bills even for a small purchase, however, street vendors might refuse to change large bills. Only Japanese yen are accepted in Japan. You cannot pay for your transactions in any other currency. Most drink vending machines accept 1,000 yen notes and coins. You can also pay with large bills and with coins at most ticket vending machines at train and metro stations. On busses only coins are accepted. However, it is usually possible to change 1,000 yen notes at the cashier box near the driver's seat.
You can withdraw Japanese yen with credit cards issued by a foreign financial institution at international ATMs of JP Bank, which is the bank of Japan's post office, and at 7-11 convenience stores. While most banks and other convenience stores also have ATMs, foreign credit cards are often refused. ATMs at post offices accept most cards, including VISA, VISAELECTRON, PLUS, MasterCard, Maesto, Citrus, American Express, Diners Club, JCB, Unionpay and DISCOVERY. ATMs at Seven Bank, the financial institution related to the 7-11 convenience store, accepts most foreign-issued credit cards. There are Seven Bank ATMs in all of Osaka City's 24 wards. Access this link to Seven Bank's ATM locator. For example, in Chuo Ward there are over 60 Seven Bank ATMs. Osaka Castle and the popular shopping of Dotonbori, Shinsaibashi and Amerikamura are located in this ward. Kita Ward has over 50 Seven Bank ATMs. Osaka Station and the surrounding Umeda area are home to some of Osaka's largest department stores, including Hanshin Department Store, Hankyu Department Store and Daimaru Umeda. Most ATMs are not open for business for 24 hours. Hence pay attention to the opening times of ATMs at post offices and convenience stores as there are some access restrictions in the early mornings, evenings and on holidays. Often there is also a withdrawal limit. This limit varies. Sometimes it is just 10,000 yen, sometimes up to 200,000 yen. Usually there is also a service charge per credit card transaction.
Credit cards issued by foreign financial institutions can increasingly be used for purchases in department stores, retail stores, electronics retailers and for buying train tickets at the reservation counters. VISA is the most widely accepted card.
You can buy yen or exchange money at foreign exchange counters at banks, large hotels and inns and at authorized money exchangers, such as Travelex, for example at Kansai International Airport. You can also cash in Travelers Checks there. At stores Travelers Checks are usually not accepted except for few large department stores and electronics retailers. Another way to get Japanese yen in Japan is via money transfer using Western Union. You can transfer money to, and also from Japan to your home country, via the Seven Bank ATMs Western Union service.
If you stay longer in Osaka, it might be worth to get Kansai's re-chargeable smartcard, called ICOCA. This card is useful when travelling around Osaka and the neighboring cities of Kyoto, Kobe etc. as you can pre-load it with a larger amount of money which safes you the trouble of paying tickets individually. What's more, it can also be used for making purchases around Osaka's large train stations.