Hiroshi Kumagai, head of the New Conservative Party, the junior coalition partner of the Liberal Democratic Party, lost his seat in Sunday's general election.
Kumagai, 63, had been seeking re-election to the House of Representatives in the No. 7 district of Shizuoka Prefecture, but trailed independent newcomer Minoru Kiuchi, 38, a former diplomat who received full backing from the LDP's Shizuoka prefectural chapter.
"I received this judgment from the people and I must accept it solemnly," Kumagai said.