One vote in the least-populated single-seat constituency for the lower chamber of Japan's parliament is at least twice as powerful as one in the eight most populous constituencies, Jiji Press has determined based on official population data for 2024, raising questions about the constitutionality of such wide vote-value disparities.

The number of such House of Representatives constituencies has increased from the previous year's four. The Lower House has 289 single-seat electoral districts.

According to the internal affairs ministry's latest basic resident register data released earlier this week, a single vote in the Tottori No. 1 district carries 2.080 times as much weight as one in the Fukuoka No. 5 district, 2.048 times that of one in the Fukuoka No. 3 district, and 2.038 times that of one in the Ibaraki No. 6 and Kyoto No. 6 districts. The four constituencies' vote-value disparities already exceeded 2.0 as of last year.

This year, the figure reached or topped the threshold for courts finding an election result unconstitutional in four more constituencies — the Fukuoka No. 2 district, at 2.023; Hokkaido No. 2, at 2.010; Miyagi No. 2, at 2.002; and Aichi No. 12, at 2.0.

The revised public offices election law took effect at the end of 2022, redrawing constituency boundaries for a total of 140 single-seat Lower House constituencies in 25 of 47 prefectures in the country, including 15 prefectures where the number of seats were either reduced or increased. The new electoral map is set to be applied from the next Lower House election.

The boundary revamp initially helped reduce the maximum vote-value disparity to 1.999, based on the 2020 national census.

For the House of Councilors, the largest vote-value disparity is found in Kanagawa Prefecture, at 3.041. Disparities also exceed 3.000 in Miyagi Prefecture, at 3.012, and Tokyo, at 3.005.