Tokyo Gov. Yuriko Koike stepped down Tuesday as leader of the Party of Hope amid her waning grip on power in the fledgling party she founded, in the wake of its poor performance in last month's general election.

"I want to leave national political matters to Diet members. In that sense, I'm the founder, but I will step down as representative and support you all in an appropriate manner," Koike said at a party general meeting at which its new leadership was endorsed.

The party leader post was filled by Yuichiro Tamaki, a lower house lawmaker who last week was selected as the party's co-head alongside the 65-year-old governor.

"After witnessing the start of Mr. Tamaki's leadership lineup, one of my responsibilities as the founder came to an end," she told reporters after the gathering.

Tamaki expressed hope Koike will continue to be involved in managing the party as an adviser.

Koike has said she wanted to concentrate on her job as Tokyo governor following what she described as an "utter defeat" in the general election.

Koike, who served as defense and environment ministers when she was a Liberal Democratic Party member, established her national political party in the run-up to the Oct. 22 House of Representatives election in an effort to defeat Prime Minister Shinzo Abe and his ruling coalition.

There had been speculation that the first female governor of Tokyo would run in the general election as a step toward becoming the first female prime minister of Japan.

But she came under criticism for doubling as a national political party leader and governor. Koike left the ruling LDP to run in last year's gubernatorial election.

The Party of Hope absorbed a number of lawmakers from the Democratic Party after former leader Seiji Maehara decided to disband the then main opposition party to enable its members to run as candidates for Koike's party.

But Koike apparently alienated some voters when she said she would "exclude" left-leaning members whose views differed from her on such issues as national security and possible revision of Japan's pacifist Constitution.

The Party of Hope fielded 235 candidates nationwide but managed to secure just 50 of the 465 seats up for grabs, trailing the Constitutional Democratic Party of Japan, which became the largest opposition force by securing 54 seats in the election. The members of the CDPJ include those who were rejected by Koike.

On Tuesday, the party accepted Maehara, who had left the Democratic Party, as a new member, bringing the total number of its lawmakers to 54, including three in the House of Councillors, or upper house.

Abe's LDP secured a two-thirds majority in the lower chamber with its junior coalition partner the Komeito party.