YouTube, the booming American Web site where surfers share short videos, is taking off in Japan, too. The number of Japanese visitors per month has more than quadrupled to 6.4 million since February, an unprecedented success for an English-language Web site. Recently, clips of television shows on a celebrity scandal received 3 million hits in just a matter of days.

“It just shows how much people want to see certain videos,” and how utterly others have failed to find the content Japan really wants, says Yoshikazu Tanaka, president of GREE, a social networking Web service. YouTube is shaking the staid world of Japanese broadcasters. When Japanese Internet ventures like Rakuten and Livedoor have tried to buy TV stations for their content, they’ve been swatted down by big media companies. But the popularity of YouTube, which limits videos to a few minutes, has caught broadcasters by surprise, and so far remains.