The proportional representation system that allows voters to either choose candidates by name from party lists or simply vote for the parties themselves is constitutional, the 15-member court said in a unanimous decision.
The Supreme Court's first ruling on the system came in response to a suit by a group of Tokyo, Chiba and Kanagawa voters who claimed it failed to reflect the public will in violation of the Constitution, saying the selection of a candidate and that of a party should be considered different.
Voters were first allowed to choose either a party or one of its candidates under the proportional representation system in the July 2001 election.
Under this system, seats are given to parties in line with the proportion of votes they gain and the winners on each party's list are decided according to the votes won by specific candidates.
Liberal Democratic Party Secretary General Shinzo Abe hailed the top court's decision as "appropriate."
Abe said the system is rational, is widely used by other industrialized democratic countries and does not pose any problem under the Constitution.
The court also endorsed the disparity in the number of voters per Upper House seat between the least and most populated districts for the July 2001 election.
The number of voters per seat in largest district was 5.06 times that for the smallest.
This decision was in response to three suits by the Tokyo, Kanagawa and Chiba groups, who claimed that the size of the disparity was too great to be constitutional.
The Supreme Court in earlier rulings said that a disparity of 6.59 times for a 1992 Upper House election was unconstitutional after accepting a lower disparity of 5.85 times in a 1986 election.
Six of the 15 justices voted against the majority decision to endorse the 2001 disparity of 5.06 times.
Freezes on Diet payThe ruling and opposition parties agreed Wednesday to resume talks on freezing the salaries of Diet members who are indicted on criminal charges and detained.
The agreement came at a meeting of Diet affairs committee chairmen from the LDP, its coalition partner New Komeito and the opposition Democratic Party of Japan, participants said.
The LDP, which proposed the resumption, apparently wants to prevent the party from coming under fire during the Diet session that convenes Monday over alleged vote-buying by LDP lawmakers, sources said.
The LDP was reluctant last year to accept a request by the DPJ and New Komeito to suspend the salaries of detained lawmakers.
Currently, a Diet member receives 1.24 million yen a month, in addition to 1 million yen to cover communications and travel expenses.
In the discussion last year, the LDP offered to suspend payment of the communications and travel expenses for lawmakers under detention, but rejected the DPJ-New Komeito proposal to freeze salaries.
Hiroshi Kondo, who won a House of Representatives seat on the LDP ticket in the general election in November, recently resigned after being arrested in connection with vote buying.
Another LDP lawmaker, Masanori Arai, has been arrested in a similar scandal. Arai has not given up his Diet seat.