Abstract: A seat belt retractor including a main body, a spindle rotatably journaled to the main body having a seat belt wound around the outer periphery thereof, a stopper having teeth formed at the top end thereof for engaging with external gear to inhibit the rotation of the external gear, a solenoid plunger associated with a switch in buckle parts fitted to the seat belt, a friction plate having a pair of spaced first and second projections and a recess formed therebetween with an inclined edge for controlling the movement of the stopper in such manner that, when the solenoid plunger is not actuated, the stopper is located in a non-engaging position to the external gear to enable freely pulling out and rewinding of the seat belt. When the solenoid plunger is actuated by the operation of the buckle parts, the first projection or the inclined edge of the friction plate inhibits the stopper from engaging with the external gear to allow the rewinding of any slack of the pulled out seat belt.