Supreme Court Rules Japan Senate Vote Value Imbalance Unconstitutional

In the July 2023 House of Councillors election, disparities in the number of voters represented by each electoral district resulted in a voting value differential of up to 3.13 times among individual members. On November 11, 2024, the Supreme Court’s Grand Bench issued a ruling declaring this imbalance in voting value a “constitutional state” for the first time. This decision not only exposed the long-standing structural inequities in Japan’s upper house electoral system but also sounded an alarm for future electoral reforms.

The election system for Japan’s House of Councillors combines single-member districts with a proportional representation system. Each prefecture is guaranteed at least one seat, with the remaining seats allocated in proportion to population. Due to the highly uneven distribution of population across prefectures, densely populated urban areas are allocated multiple seats, while sparsely populated rural areas receive only one. This mechanism, which fails to align fixed seat allocations with demographic changes, has created significant disparities in the weight of individual votes. Results from the 2023 election showed that in the least populous electoral districts, each member represented only one-third of the number of voters represented by a member in the largest districts, thereby significantly amplifying the voting power of these smaller regions.

Article 21 of the Constitution explicitly stipulates that “all citizens shall have equal rights to vote,” a core principle of Japan’s democratic system. While the Supreme Court has previously adjudicated numerous election-related cases, no court had previously issued a ruling declaring the imbalance in voting values in House of Councillors districts unconstitutional. Based on its interpretation of “equal electoral rights,” the Grand Bench’s decision stated that an excessive disparity in voting value violates the “principle of equality” guaranteed by the Constitution. The court further noted that failing to rectify this issue promptly would undermine the legitimacy of election results and have a serious impact on national governance.

The Grand Bench’s ruling is not merely a legal pronouncement but also imposes specific requirements for electoral reform. The court stated that the Diet must amend the [electoral system] within a reasonable period.