Liberal Democratic Party lower house lawmaker Toshinao Nakagawa quit the ruling party on Friday following reports of his involvement in an extramarital affair.
Nakagawa, who resigned earlier this week from his post as parliamentary vice economy, trade and industry minister, was urged by the LDP's executives to voluntarily leave the party amid stalled Diet deliberations.
On Friday, he gave notice of his departure and the party accepted it.
The main opposition Democratic Party has also been seeking Nakagawa's resignation from parliament and will continue to pressure him to do so. But the government's top spokesman, Yoshihide Suga, said Thursday it is up to Nakagawa to decide what course of action to take.
Nakagawa effectively admitted to the affair Tuesday in a Facebook post in which he apologized to constituents for his "lack of virtue."
"I want to spend the rest of my life redeeming myself to my wife and family," he wrote in another post Thursday.
He denied specific allegations made by Japanese tabloid media that he had lived a double life with another woman and was reported to the police for stalking.
Nakagawa was elected to the House of Representatives in 2012 from a constituency in Hiroshima.
His father is Hidenao Nakagawa, a former LDP lawmaker who once served as chief Cabinet secretary.© KYODO