Shigenobu Fusako, a former leader of the now disbanded Japanese Red Army militant group, was released from prison after serving her 20-year sentence.
Shigenobu, now 76, was convicted and sentenced to 20 years in prison for her involvement in the 1974 seizure of the French Embassy in The Hague, Netherlands.
It was one of many terrorist attacks staged by the leftist group around the world in the 1970s and 1980s.
Shigenobu left a medical prison in Tokyo by car on Saturday. She was greeted by about 20 of her supporters outside the prison. Some protesters also gathered in the area.
Informed sources say that while she was in prison, Shigenobu underwent four operations to treat cancer.
She told reporters she would like to apologize for the hurt she and her group have inflicted during hostage takings and other incidents. She said she hoped to focus on overcoming her illness while reflecting on her past.
Shigenobu disbanded the militant group in 2001 while she was in prison. However, seven of its members are still at large.
Japanese police have released video and images of the fugitives in a bid to gather information about them. They believe the group remains a threat to public safety and plan to continue monitoring Shigenobu.