The Supreme Court ruled Oct. 5 that the 2004 Upper House election was carried out in a constitutional way, despite a 5.13-fold disparity in the weight of one vote between the most populated electoral district and the least populated one.

But the Grand Bench's 10-5 ruling holds the Diet to rectifying the situation. The ruling said that continuing efforts by the Diet to reduce disparity, including a review of the current elections system, are in line with the spirit of the Constitution. The Diet should take this as a call for speedy action to change the election system so that vote-weight disparity, if not eradicated, is at least reduced to a reasonable level.

Voters in Tokyo, Chiba and Kanagawa prefectures filed the lawsuit, saying the Upper House election held in July 2004 was unconstitutional. In that election, the number of voters per seat in Tokyo, the most populated electoral district with a population of about 12 million, was 5.13 times greater than in Shimane Prefecture, the least populated district with a population of about 600,000. The plaintiffs said the disparity violated Article 14 of the Constitution, which assures equality under the law for all people.