In order to work whilst on a student visa in Japan, international students must first apply through the university for permission to engage in part-time work. Once their application has been approved, international students may work for no more than 28 hours per week.
In general, the types of jobs open to international students are dependent on their Japanese-language ability. Students are no permitted to work at bars, night clubs, pachinko and mahjong parlors, adult entertainment shops and other similar venues.
For more information, see the JASSO website.