Japan’s Supreme Court has found that differences in the weight of votes at last year’s upper-house election had reached a state of unconstitutionality, while rejecting requests to invalidate the results.
The court’s Grand Bench said the maximum disparity between constituencies was 3.13 to one at the election on 20 July 2025. It concluded that the imbalance was sufficiently serious to raise a constitutional question and that parliament’s efforts to reduce the gap had stalled.
The decision, delivered on 11 November, does not mean that the election results have been cancelled. The court said the seat-allocation rules had not been shown to have become unconstitutional at the time of the vote, and dismissed the appeals seeking to overturn the election.
What the disparity measures
The figure compares the number of eligible voters per elected member across constituencies. In the 2025 contest, Kanagawa had the highest number of voters per member and Fukui the lowest. The 3.13-to-one gap meant that, in this measure of representation, a vote in the more heavily represented constituency carried considerably more weight than one in the less heavily represented constituency.
The challenge concerned the allocation of constituency seats, rather than the counting of individual ballots. Japan’s House of Councillors, the upper chamber of the national parliament, combines constituency elections with proportional representation. Members serve six-year terms, with half of the chamber elected every three years.
Two groups of lawyers brought 16 cases across Japan, arguing that the disparity breached the constitutional requirement for equality of voting value and asking courts to invalidate the election. Election commissions argued that the gap had increased only slightly.
Before the Supreme Court’s decision, high courts and their branches had produced differing assessments: 11 rulings found that the election was held in a state of unconstitutionality, while five found the arrangements constitutional.
Why the results stand
Ten of the 15 Supreme Court justices supported the finding that the 2025 disparity had reached a state of unconstitutionality. The other five considered the arrangements constitutional. The justices agreed on dismissing the appeals.
In its reasoning, the court distinguished a serious imbalance that raises a constitutional problem from a finding that the relevant seat-allocation rules themselves had become unconstitutional. It said earlier Supreme Court decisions after electoral changes had not found the upper-house vote gap to be in such a state before the 2025 election.
Against that background, the court concluded that parliament’s failure to amend the allocation rules before that election could not be said to have exceeded the limits of its discretion. The requests to invalidate the election therefore failed.
The majority nevertheless criticised the lack of progress towards a further reduction in the disparity. It noted that the maximum had grown from 3.03 to one in the 2022 election, despite an earlier judgment calling further correction an urgent issue. It said discussions had continued without a concrete prospect of agreement on further reform.
A long-running representation issue
Japan previously combined two pairs of less-populated prefectures into joint constituencies to reduce the gap: Tottori with Shimane, and Tokushima with Kochi. Those arrangements were introduced for the 2016 upper-house election and remained in place for the 2025 vote.
Following the mergers, the Supreme Court had found the disparities in the 2016, 2019 and 2022 upper-house elections constitutional. The maximum gap was 3.08 to one in 2016 and 3.00 to one in 2019.
The last time the court had found an upper-house election to be in a state of unconstitutionality was after the 2013 vote, when the maximum disparity was 4.77 to one. The latest judgment is the first such finding for an upper-house election since the constituency mergers.
The judgment leaves the existing election result in place while setting out the court’s assessment of a problem that parliament has debated for years. It does not itself prescribe a new map or choose a particular method for reducing the difference between constituencies.
