On September 2^nd of 1998, the Supreme Court ruled on the constitutionality of the Upper House election which took place in July 1995. The difference in the value of the votes has been an issue since the 1960s. Arguably, a large difference in the value of votes would be against the equal treatment provision (Article 14) of the Constitution. Initially, the Supreme Court maintained that the allocation of seats among the constituencies was a matter of legislative policy. In 1976, the Supreme Court rendered a ground-breaking judgement in which it ruled that in cases where the inequality of the value of the votes is such that it cannot be justified even by taking into account various factors which are normally considered by the Diet, and the required reform has not been implemented within a reasonable period, it is unconstitutional. The Court found the 5 against 1 difference to be unconstitutional. On the other hand, the Court did not avoid the election, resorting to a provision in the Law on Administrative Litigation which allows the court to declare a certain act of the government to be unlawful, but to maintain its effect on the ground of public welfare.

Since then, there has been a series of judgements on the constitutionality of various elections. In 1996, the Supreme Court found the difference of 6.59 against 1 in the Upper House election to be unconstitutional. In the meantime, the Diet was slow in taking measures to rectify the inequality. It was only in 1995 that the Law on Public Election was amended and the difference of the value was reduced from a maximum of 6.48 against 1 to 4.81 against 1. In this present case, the constitutionality of the Upper House election which took place soon after this amendment, in which the difference in the value was 4.97 against 1, was contested.