Abstract: The invention relates to a device for automatically retracting and winding up a seat belt for use in a vehicle to protect the occupant and in particular the device controls the force for retracting or winding up the seat belt. The device includes a frame with a winding reel rotatably supported by the frame with spring means connecting the frame and winding reel. The winding reel is adapted to wind thereon a seat belt with a spring force of at least one main and auxiliary springs with a spur gear rotatably supported by the winding reel and operatively interposed between the main and auxiliary springs for changing the winding force and means for detecting a wound quantity of the seat belt.