Yuko Obuchi, the minister in charge of tackling declining childbirths, said Sunday she is pregnant with her second child.
According to the Cabinet Office, it is the first time a Cabinet member has become pregnant.
"My son will have a younger brother or sister," the 35-year-old Obuchi, the second daughter of the late former Prime Minister Keizo Obuchi, told a gathering of her supporters in Tomioka, Gunma Prefecture.
She said the baby is due at the end of September.
"Irrespective of myself being a minister or prospects of an election, I'd like to give birth to a healthy child," Obuchi said.
A House of Representatives member from the Liberal Democratic Party, Obuchi became the youngest postwar minister when she joined the Cabinet under Prime Minister Taro Aso at age 34 last September.
Obuchi gave birth to her first child in September 2007 after marrying a former colleague from a private broadcaster.