Belton wrote:They use the same plug design as US.
I needed to charge batteries for my camera and my Clie (for Japanese Dictionary) and had no problem using the flat two prong plugs.
There's a picture and some info here.
http://www.japan-guide.com/e/e2225.html
One important difference to note: most (i.e. almost all) Japanese plugs don't have a hole for the third "grounding" pin. The big round one at the top of the plug in this pic:
The Japanese usually use a grounding wire instead, as you can see in the middle of this picture:
So if you have any items with grounding plugs, you'll have some problems.
Also, in Canada (I don't know about the US...) if there is no grounding pin on the plug, often one of the two pins is made slightly wider than the other (so you can't put it into the outlet upside-down). As I recall, new Japanese plugs have this, but the older ones don't. So, sometimes, new Canadian devices won't fit into older Japanese outlets.
Incidentally, I believe that American-made alarm clocks don't work in Tokyo, because the Hz is different. But if you're in Osaka, they work fine. So be careful about that if you don't want to miss your train.