Cash Withdrawals & Currency Exchanges in Japan
There are 2 ways to withdraw money internationally in Japan although most Japanese ATMs do not accept credit, debit or cash cards issued abroad.
cf: The Rate of Exchange
Seven Bank ATMs
Seven Bank ATMs, located inside Seven Eleven/7-Eleven convenience stores, accept credit and debit/cash cards issued abroad. They offer vocal and on-screen guidance in English, Korean, Chinese, and Portuguese. Receipts support these four languages as well.
The advantage of Seven Bank ATMs is that they are operating 24 hours of 365 days. You can withdraw cash anytime you like.
You will find easily some Seven Eleven stores in any district in Tokyo. Some hotels have a Seven Eleven inside the building.
Search 7-Eleven on Google Maps
Post Office ATMs
Japan Post Bank ATMs accept foreign credit and debit cards and also offer a user menu on the screen in English. You can withdraw cash by this way.
There is "International ATM Service" notice around the ATM and stickers of the VISA, VISA Electron, MASTERCARD, American Express, China UnionPay, Maestro, PLUS, JCB, Cirrus, Diners Club International, and DISCOVER logos.
You will find post offices all over Tokyo and Japan. There are central post offices of the district, whose ATMs typically work from 8:00 until 23:00 (20:00 on Sunday,) and small local ones, whose opening hours are shorter than big offices. Sometimes you possibly find just ATMs in a large shopping centers, etc.
Google Maps will help you with finding the nearest post office. You go there by 16:00 on weekdays, and surely it is their business hours even if it is the smallest kind of post offices in Tokyo.
To search & learn exact business hours of each post office: http://map.japanpost.jp/pc/index.php (only in Japanese language)
China UnionPay cards are acceped at Japan Post Bank (the bank of post office,) Seven Bank, Bank of Tokyo-Mitsubishi UFJ, and Sumitomo Mitsui Banking ATMs for cash withdrawals.
Where to Exchange Currency
Banks in the arrival lobbies of Narita and Haneda International Airports offer currency exchange services, so you do not need to exchange your currency in advance of your travel in Japan.
In the cities, you can convert foreign currency into Japanese yen at banks, stores and post offices with the sign of “Authorized Money Changer."
cf: The Rate of Exchange
Other Payment Methods during your travel
It is a good idea to carry some different kinds of credit cards. (For example, take VISA and American Express cards.)
Credit cards are accepted in most hotels, shopping centers, retail shops in tourist spots, and for tickets of transportation such as JR Shinkansen (Japanese super expresses,) etc, and some taxis.
You can use Traveler's Checks at most banks, hotels and some shopping centers.