The Supreme Court's Grand Bench rules on whether the 3.13-fold vote disparity in the 2025 upper house election was constitutional, a decision that will show whether the court redraws the line it has upheld for a decade.
The ruling is due at 3 p.m. on the 11th, the Mainichi Shimbun reported. By the ratio alone, the election sits close to what has been treated as the constitutional line.
The court has repeatedly ruled on the question of whether unequal "precious votes" can be tolerated. In the past 10 years it has found elections constitutional each time.
That has left some viewing a twofold gap in lower house elections, or a threefold gap in upper house elections, as the threshold for constitutionality.
One vote, different weights
The weight of a single vote differs by district. In the July 2025 upper house election, Fukui Prefecture had the fewest voters per lawmaker, at 308,266.
Kanagawa Prefecture had the most, at 964,086. A Kanagawa vote was worth just 0.32 of a Fukui vote, a gap expressed as 3.13-fold.
The disparity widens as people move from rural areas to cities, unless the electoral system or district boundaries change. The problem is known as the "vote disparity."
"A state in which the disparity has expanded violates the Constitution, which provides for the equality of the value of votes," the plaintiffs' group of lawyers argued.
The cost of strict equality
Strict adherence to one person, one vote would sharply increase the number of seats in urban areas. The voices of rural regions could then fail to reach national politics.
For that reason both the Diet and the courts have tolerated a certain degree of disparity. In the early 2000s the Supreme Court upheld gaps of under threefold in lower house elections and around fivefold in upper house elections.