A seat belt retractor includes a seat belt winding device for winding up a seat belt by actuation of a motor and a control unit. The control unit, under a predetermined condition, repeats a process of stopping the actuation of the motor when an overload of the motor is detected and restarting the actuation of the motor after a lapse of a predetermined time period. The control unit includes a timer for clocking the time period from the start to the stop of the actuation of the motor, a counter for counting up the number of times of starting the actuation of the motor, and a determination module that based on the result of the timer and the counter determines whether or not actuation of the motor, which is stopped by the detection of an overload, is to be restarted.