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Japan’s Top Court Upholds 2024 Lower House Election, Backs Adams Method Redistricting

A four-judge panel found the Diet’s new seat-allocation system reasonable, pointing to stable reduction of vote disparities under the Adams method.

Overview

  • The Supreme Court’s Second Petty Bench on Sept. 26 dismissed appeals by two lawyer groups seeking to void the 2024 vote and ruled the election constitutional.
  • All 16 high courts had reached the same conclusion, and the case was not referred to the 15-judge Grand Bench for the first time in 24 years.
  • The 2024 contest was the first to apply the Adams method through a 10-increase/10-decrease redistricting that shifted seats to urban areas and yielded a maximum vote-value gap of 2.06.
  • The majority said the new framework aims to keep disparities substantially reduced over time and found no severe imbalance beyond effects from population movement.
  • Justice Junichi Takasu issued an individual opinion calling the system in an unconstitutional state due to likely rapid demographic shifts, while plaintiffs warned the small-bench ruling could ease pressure on the Diet to keep reviewing districts.