The three men running for president of the Democratic Party of Japan vowed Thursday in Tokyo to boost the number of female lawmakers as a way to make the largest opposition force strong enough to challenge the ruling Liberal Democratic Party.

Speaking at the Foreign Correspondents' Club of Japan, DPJ Deputy President Katsuya Okada, 61, pledged to publicly seek female candidates for the next Upper and Lower house elections soon after the party holds its leadership race this Sunday.

"I believe the trigger to change Japanese society and the DPJ itself is women," Okada said. "We must increase the number of women in the party's executive positions, not nominal positions but real roles where they can really do practical jobs."