Leader of the opposition Democratic Party of Japan (DPJ), Banri Kaieda, quit Monday over its failure in Sunday's general elections.
The DPJ gained 73 seats in the vote for the parliament's 475-seat lower house, 11 more compared to the 2012 elections, but Kaieda himself failed to secure a seat, Xinhua reported.
He admitted the party failed to stop the runaway policy of Prime Minister Shinzo Abe, pledging to continue protecting Japan's constitution.
During the election campaign, Kaieda criticised Abe's economic policy mix, or "Abenomics," for enlarging the country's wealth disparity.
Abe's Liberal Democratic Party and its junior Komeito partner took an overwhelming majority with 326 seats.
