Tokyo: A Japanese politician who made headlines over his quest to take paternity leave quit on Friday after admitting to an affair with a bikini model while his wife was pregnant.

Kensuke Miyazaki, 35, shook up Japan's conservative political scene when he sought to take a month's leave to help his then pregnant wife, a first for a male Japanese lawmaker.

His quest drew criticism from many politicians in a country where fathers taking time off to care for children is rare.

But Miyazaki won the backing of Prime Minister Shinzo Abe who supported his trailblazing idea.

On Friday, the ruling Liberal Democratic Party lawmaker announced his resignation after a weekly magazine revealed his affair with the 34-year-old woman while they were in Kyoto, his constituency.

He met the woman — also a professional kimono dresser — when she was helping Miyazaki and other politicians dress up in ceremonial garb for the opening of Japan's parliament last month.

The sexual encounter happened several days before Miyazaki's wife — fellow politician Megumi Kaneko — gave birth to their first child.

‘I have done such a cruel thing’ to my wife, he told a nationally televised press conference.

‘I'm deeply, deeply, deeply sorry that what I've been advocating (on paternity leave) was contradicted by my careless actions. So, I have decided to quit.’

Paternity leave is rare in Japan, with only about 2.3 per cent of men working at private companies taking time off.

Abe wants to increase the ratio to about 13 per cent by 2020, as he moves to boost the number of women in the workforce to kickstart the struggling economy.