Laws in the United States and some European countries have already taken into account that a person may not be able to provide consent because of illness or intoxication, or that an offender could exploit a situation of authority.

Until now, because of the high bar for a sexual assault to be officially classified as rape in Japan, few victims have brought criminal charges. When Shiori Ito, a journalist, alleged that a prominent television journalist had raped her when she was unconscious and unable to give consent, prosecutors declined to file charges. Ms. Ito later won damages in a civil case against Noriyuki Yamaguchi, a former Washington bureau chief of the Tokyo Broadcasting System, when a judge accepted her account of the assault.

Activists for victims of sexual assault had long argued that Japan’s rape laws were antiquated because of the absence of any mention of consent and the low age of consent.

Earlier this year, Meiko Sanno unsuccessfully sued her former professor for sexual harassment, alleging he had taken advantage of his supervisory position to groom her for a relationship that she said she could not consent to. Lawyers and activists who support sexual assault victims have long argued that the law should account for the fact that people who fear reprisals from teachers, bosses or others with authority cannot freely consent to sex.

At a news conference after the bill’s passage on Friday, Kazuko Ito, a lawyer who has represented sexual assault victims, said it was a “great step forward.”