To be specific, Japanese sockets are compatible with North American ones. Although North American plugs are polarized - so an American plug can be inserted into a Japanese outlet. However, Japanese extension cords and taps are not, so you'd need a plug adapter to use them. (You can pick one up at a Daiso 100 yen shop - Type A). Any 3 prong American plug would need a converter as well, although those too are cheap and ubiquitous.
Europe is a different story - you'll need both a plug adapter as well as a voltage converter. You can pick one up either in Europe or Japan - I can't say which country would be cheaper. In Europe at least you would not have any language problems explaining things.
sockets are the same but voltage may be different. You should watch each appliances if it's compatible to voltage in Japan. (100～110V)