Assemblyman Akihiro Suzuki, of the ruling LDP party, admitted responsibility for heckling assemblywoman Ayaka Shiomura of the minority Your Party, yelling in the midst of her speech, "You should get married!"
Suzuki publicly apologized on Monday.
Another voice, who has not yet admitted involvement, jeered during the speech, "Can't you even bear a child?"
While Shiomura accepted Suzuki's apology, she said, "I'm positive that there were others besides Mr. Suzuki who made comments."
After finishing her June 18 speech, Shiomura later posted on Facebook that the sexist remarks shouted by her fellow assemblymen were like "a punch in the gut."
The incident sparked a public debate in Japan, where sexism in the workplace is common and men are paid 30 percent more than their female counterparts.