TOKYO, Oct. 30 (Xinhua) -- Seiji Maehara, head of the collapsing Democratic Party (DP) of Japan, resigned on Monday over his fatal decision to merge his party with the Party of Hope before the lower house election on Oct. 22, which effectively split up the opposition forces and offered the ruling camp a comfortable win.

The DP, once the main opposition party of Japan, accepted Maehara's resignation on Monday and was set to elect a new leader on Tuesday, while Maehara said he will leave the DP and join the Party of Hope after the resignation.

Maehara, elected as leader of the DP in September, decided to effectively merge the Democratic Party with the Party of Hope led by Tokyo Governor Yuriko Koike after Prime Minister Shinzo Abe dissolved the lower house on Sept. 28 for a snap election.

However, Koike, sharing the ruling Liberal Democratic Party's conservative views on constitutional reform and security laws, refused to accept the liberal wing of the DP into her party.

Some liberal members of the DP led by former Chief Cabinet Secretary Yukio Edano established the Constitutional Democratic Party of Japan (CDPJ) to combat the conservative forces in the lower house election, while some others ran as independents.

Benefiting from the split-up of the opposition forces, Abe's ruling camp won a two-thirds "super majority" in the lower house election, while Koike's Party of Hope took only 50 seats, less than the 57 seats before the election.

The CDPJ ended up taking 55 seats after taking in a member who ran as independent in the election and became the main opposition party in the lower house.

The still extant DP comprises 46 members of the upper house of parliament, and 18 lawmakers who ran as independents in the lower house election, as well as its regional chapters.