The Social Democratic Party on Thursday approved House of Representatives lawmaker Kiyomi Tsujimoto's secession from the tiny opposition force, refraining from punishing her for leaving.
The approval came after the SDP considered whether to punish her since she announced her plan in July to become an independent lawmaker.
SDP Secretary General Yasumasa Shigeno said the party has given consideration to a request from the party's Osaka chapter to take into account her past contributions to the party.
Tsujimoto, 50, was elected to the Lower House from one of the Osaka Prefecture constituencies for the fourth time in the chamber's general election last August.
She served as senior vice minister of land, infrastructure, transport and tourism before the SDP left the Democratic Party of Japan-led ruling coalition.