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.