You won't need any adapters for your plugs, but if you are staying in more traditional lodgings (such as ryokan or minshuku), you may not be able to find a three-prong (grounded) outlet. Two prong plugs are more common in such lodgings. My husband and I use the flip out two-prong plugs that come with the Mac power bricks when we travel in Japan.

We've also had the situation arise in ryokan and minshuku where there is only one plug for the entire room, so if you have multiple devices to plug in, you may want to bring or buy an extension cord.

Posted Apr 22, 2012

Gretchen's answer was good. Their voltage is 100 instead of 120 (as in North America) but when I lived south of Tokyo it was never an issue. See additional info using link below for other details.
http://www.japan-guide.com/e/e2225.html

Posted Apr 24, 2012

Heads up about the internet. wi-fi is really hard to find in most places minus youth hostels and such.so don't be too frustrated if you end up sans-internet for a while.

Posted May 07, 2012