Tokyo - Japan's first female candidate for leader of the ruling Liberal Democratic Party (LDP) said Friday that she had won the support of former prime minister Junichiro Koizumi.

"I am super happy," said Yuriko Koike, who faces four opponents in the September 22 LDP vote. "With strong cheers from Mr Koizumi, I gained power to 100 per cent."

If Koike prevails in the race, she would become the nation's prime minister. The LDP president is assured to assume the nation's top job because the ruling party controls the more powerful lower chamber of the Japanese parliament and can override upper house decisions.

Charismatic Koizumi declared his full support for the 56-year-old Koike Friday by saying she would be the perfect opponent against Ichiro Ozawa, leader of the opposition Democratic Party of Japan (DPJ).

The next LDP president would lead the party against the DPJ in a House of Representatives election likely to be held in a few months.

"I will support Ms Koike," Koizumi said. "I'll cast a ballot for her."

While Taro Aso, LDP secretary general, was regarded as the front-runner to succeed outgoing Prime Minister Yasuo Fukuda, Koizumi's open support for Koike might boost her chances of a win.

Koike, who served as environment minister in the Koizumi cabinet, continued to push for structural reforms initiated by her mentor. Koizumi served as premier from 2001 to 2006. (dpa)