Electoral system for national legislature

The Political Participation and Constitution in Japan by Shigenori Matsui, http://www.juridicas.unam.mx/wccl/ponencias/1/27.pdf

The number of House of Representatives is set at 475: 295 members are elected from single-member election districts and the remaining 180 members are elected through proportional representation. The voter votes on two ballots: one for a candidate in the election district and other for a political party in proportional representation.