When end lock has occurred in a seat belt retractor due to winding-up of a webbing, the end lock is easily and surely released. A stop part (6G) engages with a lock arm (40) displaced in a locking operation direction and stops the lock arm (40). A lock mechanism (9), in a state where the lock arm (40) stands still on the stop part (6G), starts operation with rotation in a pull-out direction (P) of a winding drum and stops rotation of the winding drum. A transmission mechanism (19) transmits rotation of the winding drum to the lock arm (40) and displaces the lock arm (40) in a release direction to release the engagement with the stop part (6G) is released between the time when operation of the lock mechanism (9) is started and the time when rotation of the winding drum is stopped. Release means (18) releases the engagement between the lock arm (40) and the stop part (6G) by the transmission mechanism (19).