The Osaka High Court on Thursday ruled that the House of Representatives election in December, in which there was a maximum 2.13-fold disparity in the weight of votes between districts, was constitutional.
The court dismissed the plaintiffs' demand that the election results in Nara Prefecture's No. 4 district be nullified. A lawyers' group, which filed the lawsuit, plans to appeal the ruling to the Supreme Court.
The plaintiffs argued the Constitution's guarantee of equality under the law was violated by significant variation in the population of voters in single-seat districts.
In the ruling, presiding Judge Atsushi Tanaka said: "The disparity was only somewhat over two-fold after the Diet cut the number of single-seat constituencies to 295 from 300."
The judge also said the vote-value disparity is "not in a state violating the legal equality guaranteed by the Constitution."
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.
Two groups of lawyers have filed a total of 17 lawsuits across the country over vote-value disparities in the December election. By Wednesday, 11 high courts had issued rulings, with one having judged the election as unconstitutional, seven as being "in a state of unconstitutionality" and three ruling it constitutional.
Other rulings on similar suits are expected to be issued by the end of April. Under the law, lawsuits involving the validity of national election results bypass district courts and are initially tried at high courts.