www.mixi.jp is the original Japanese social networking site and it is the most popular in japan. It is setup for Japanese cell phone(keitai) access and more than half of the members use it only from their cell phones. I have been told it is difficult to get a membership outside of Japan because they want a Japanese ketai mail account for registration and it is by invitation only. I have heard that it use to be open to anyone. perhaps someone from Japan with a mixi account can tell you more about it. George.

many people is joining. but Everyone can not participate. Participant's invitation mail is needed. I also am participating. Are a lot of people in the foreign country also participating, and with whom can it make friends?

What George said is almost everything about mixi. There are some functions that facebook doesn't have. But they don't make any big differences for me. People who don't live in Japan used to be able to join mixi if they have an invitation email. However, as George said, a Japanese mobile email address is required now.