In spite of its technology-driven economy, Japan is still very much a cash-based society. Though credit cards are increasingly popular, foreigners should not expect to have much luck with them outside of major cities.
Japanese ATM service is provided through a combination of traditional ATM machines and CDs (cash dispensers) that only process withdrawals. ATMS and CDs are common in major cities, but do not usually accept foreign debit and credit cards unless they are operated by an international bank such as Citigroup. Outside of the cities, ATMs become less common and it is practically impossible to use them with a foreign card. The best way to ensure you have access to cash is by setting up a post office savings account.
Postal ATM operating hours then decrease proportionally to the size of the post office, from major post offices (typically 7:00 to 23:00, shorter hours on weekends) to medium sized offices (typically 8:00 to 20:00, shorter hours on weekends, possibly closed on Sundays) to minor offices (typically 9:00 and 16:00, closed on weekends).
Many Japanese ATMs are not open for 24 hours, either. They are actually turned off at night (usually 19:00 during the week, 17:00 on Saturdays). While this might seem strange to foreigners, it is not considered unusual in Japan: cigarette machines are also turned off at night.
7-Eleven convenience stores, however, do provide ATMs with 24-hour service. They also accept international credit and debit cards.
Attention! you can withdraw cash 24/24h with the some machine which is located in convenience stores, or stations, but you will be charged about 2$ for each operations if you do while bank closing time includes week-ends.
Please check your bank regulations.
Banking in Japan : At postal giant, friendly service and low fees (NY times travel)