Japan's government promised Tuesday to examine the country's voting system after courts ruled that some general election results were unconstitutional and invalid.
Over two days of hearings, judges in western Japan said the huge disparity in the number of electors in different constituencies meant the value of each vote varied too greatly to be fair.
Despite the rulings, which affect three seats, the results from last December's general election which swept Shinzo Abe to power will not immediately be overturned.
The decisions are effectively suspended until the supreme court rules on them, an event scheduled for some time towards the end of the year.
"We humbly accept the court ruling and will take appropriate measures after having a close look at it," Chief Cabinet Secretary Yoshihide Suga told a news conference.
This week's rulings were the latest in a series of victories for a group made up mainly of lawyers and constitutional scholars who claim not to have a party political axe to grind.
Previous court hearings have declared elections to be "in a state of unconstitutionality" but have allowed results to stand. Monday's finding in Hiroshima was the first time the result has been declared invalid.
Observers say the legal challenges are aimed at bringing moral pressure on politicians of all parties to alter an electoral system that has become weighted in favour of those living in rural areas.
Activists want constituency boundaries redrawn to better reflect the current population distribution, which has changed dramatically over the last few decades as Japan urbanised.
Commentators said Japan's ingrained tendency to seek consensus means the situation is likely to be rectified long before it gets to the point where the supreme court overturns an election result.
"The verdict on Monday is a message from the judiciary that politicians should lose no time in reforming the constituency system," said Mikitaka Masuyama, professor of politics at the National Graduate Institute for Policy Studies.
But he said any attempt to equalise the vote value of Japan's densely populated cities with the emptying countryside risked creating geographically vast constituencies whose inhabitants have little in common.
"If you pursue narrowing the disparity in voting power per person, it means a sparsely populated region has a huge district while a densely populated city has several very tiny districts," he said.