Editorial: Japan court ruling on vote-value disparity is a stern warning to Senate

The Supreme Court has ruled that the 2023 Senate election, characterized by a vote-value disparity of 3.13 to 1, was unconstitutional. This is a stern warning to the Diet for its failure to address the persistent issue. Disparities exceeding a 3 to 1 ratio have been deemed unconstitutional since the 2016 election. The court expressed grave concern over the Diet's lack of progress in implementing measures to improve the situation.

Previous elections with disparities of 5.00 to 1 in 2010, 4.77 to 1 in 2013, and 3.13 to 1 in 2023 were found unconstitutional. Mergers of electoral districts were introduced following these rulings, but the gap between districts has gradually widened. The merged-constituency approach had its limits, and supplementary provisions to the Public Offices Election Act required a fundamental review and a conclusion before the 2019 election.

The court's patience has run out, and attention will now turn to the Diet's response. The merged constituencies have also led to declining voter turnout, as population concentration in urban areas and depopulation in rural regions continue. Reform beyond minor fixes is indispensable, and a debate on the role of the upper house in the bicameral system is necessary.

The Senate, serving six-year terms, must function as a chamber of deliberation and reconsideration, establishing an electoral system that aligns with these roles. The issue is fundamental to the very foundations of democracy, and the Diet must accelerate debate toward fundamental reform within the next two years before the next Senate election.