Japan's NHK broadcaster reported that former Prime Minister Yoshihiko Noda was elected on Monday as leader of the main opposition party, the Constitutional Democratic Party (CDPJ), during the party's convention earlier in the day.

In the first round of voting, Noda led with 267 votes, followed by the founder of CPDJ and former chief cabinet secretary Yukio Edano with 206.

The party's current leader Kenta Izumi came in third with 143 votes, while  Harumi Yoshida, the sole female candidate, came in fourth with 122 votes.

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In the second round, where only the top two candidates participated, Noda won with 232 votes, surpassing Edano’s 180.

The outcome of the second round was determined by the party’s 136 Diet members, each holding two votes, as well as 98 endorsed candidates for the next parliamentary session and representatives from all 47 prefectures in Japan.

At a hotel in Tokyo, the CDP held its leadership election during a special party convention, with Izumi’s leadership set to conclude at the end of this month.

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With a new leader, the CDP will aim to unseat the ruling Liberal Democratic Party (LDP) and Komeito coalition in the next Lower House election.

The conservative LDP has ruled the country for decades, holding the majority of seats in parliament.

Japan's parliament will formally elect a new prime minister on October 1, an LDP official announced earlier this month.

Given their parliament majority, the winner of the LDP election is likely to become premier.