The Okayama branch of the Hiroshima High Court ruled Tuesday that the results of the 2014 House of Representatives election were "in a state of unconstitutionality" due to disparities in the weight of votes between constituencies, but it rejected the plaintiffs' demand to nullify them.
The ruling over five constituencies in Okayama Prefecture was the last in a series of 17 similar lawsuits filed across Japan against vote disparities of up to 2.13-fold in last December's general election.
Among the 17 rulings, Tuesday's decision was the 12th that questioned the constitutionality of the 2014 election.
Only one of the 17 rulings declared the contest unconstitutional, although it stopped short of nullifying the results. The other four judged it as constitutional.
In Tuesday's ruling, presiding judge Noriyoshi Katano said the vote weight disparities in Okayama were in a state that runs contrary to the constitutional call for maintaining the equality of votes.
"But it cannot be said that the Diet efforts to redress the situation were not reasonable," the judge said.
The vote weight disparity in last December's lower house election was 2.13-fold between Tokyo's No. 1 district, the country's most populous single-seat constituency, and Miyagi Prefecture's No. 5 district, the least populous constituency, according to government data.
Vote weight disparities in Japan were brought into focus after the Supreme Court said the 2.30-fold gap in the 2009 general election and the 2.43-fold gap in the 2012 election were both "in a state of unconstitutionality." It urged the government to scrap the current system of granting one seat each to 47 prefectures without paying attention to population.
The legislature, meanwhile, enacted a law in 2012 to rezone single-seat constituencies of the lower house and reduce the number to 295 from 300.
The top court is expected to issue its ruling by the end of the year.