2025 House of Representatives Election Invalidation Case (Population Disparity)

Following Japan's October 2024 general election, a voter group led by Professor Hiroshi Kamiwaki filed a lawsuit seeking invalidation of the House of Representatives election, arguing that the maximum 2.06-fold disparity in vote weight between densely and sparsely populated districts violated the constitutional principle of equality. The case, docketed as Reiwa 7 (Gyo-Ke) No. 2, was adjudicated by the Supreme Court's Grand Bench in 2025. The court examined whether the apportionment scheme met the requirements of Articles 14 and 44, considering the Diet's efforts to reduce disparity and the time passed since the last census.

The Supreme Court Grand Bench ruled that the election was held in an unconstitutional state due to the significant population disparity, but it unanimously dismissed the request to invalidate the election, citing the Diet's ongoing reform efforts and the absence of a prolonged period of deliberate legislative inaction.

Whether the maximum 2.06-fold vote-value disparity in the 2024 lower house election constituted an unconstitutional violation of the equality principle, and whether the election results should be invalidated in whole or in part.

The ruling reignited public and political debate on electoral reform, adding pressure on the Diet to adopt more effective measures—such as further redrawing districts or revising the apportionment formula—to equalize the value of votes ahead of the next election cycle.