Eiji Kidoguchi, 61, fielded by the Constitutional Democratic Party of Japan, has won a by-election for the House of Councilors in Iwate Prefecture's constituency.
The by-election, held Sunday, followed the August resignation of former Liberal Democratic Party member Megumi Hirose from the Upper House over allegations that one of her secretaries fraudulently received state funds as salaries.
The LDP, already shaken by public criticism of a slush fund scandal at its factions, chose not to field a candidate in the by-election.
Former Upper House lawmaker Kidoguchi, now elected to the chamber for the second time, focused his campaign on political reform, defeating his four rivals that included independent candidate Ayumi Tanaka, 53.
His term will end on July 25, 2028.
Voter turnout stood at 55.54%.
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