The July 2007 Upper House election was challenged by lawsuits claiming that the disparity in the relative value of votes between constituencies was so large that the election should be declared unconstitutional. The Supreme Court has now ruled that the election was constitutional and valid, but the Diet — which is responsible for preventing such disparity from occurring in excess — should not be complacent.

The 10-5 ruling, delivered on Sept. 30, said that although the distribution of seats was "not unconstitutional," there existed great inequality in the relative value of votes, which the Diet should rectify. In the election, the ratio of eligible voters per seat in the Kanagawa constituency to Tottori constituency was 4.86, meaning individual votes in less populous Tottori carried greater weight.

In the past, the Diet tried to narrow such disparity by changing the allocation of seats. After the July 2004 Upper House election featured a highest ratio of 5.13 between constituencies, two seats each were taken from Tochigi and Gunma constituencies, while Chiba and Tokyo constituencies both had two seats added.

Previous Supreme Court rulings suggested that Upper House elections would be constitutional and valid as long as the highest ratio was around 5. But it is significant that the latest ruling clearly stated that shuffling seats between constituencies will not serve as an adequate solution.

For the first time, the Supreme Court declared that the electoral system itself for the Upper House should be changed. In an unusual move, Chief Justice Hironobu Takesaki, who served as presiding judge, said that in view of the importance of reducing disparity in the value of individual votes, it is desirable for the Diet to take action immediately.

The Diet now faces the daunting task of devising a new electoral system for the Upper House. Preferably, the electoral system should be designed so that the Upper House will have a different character from the Lower House. The Diet should realize that if it does not act with appropriate speed, the top court may declare a future election unconstitutional and demand a do-over.