Abstract: A seat belt retractor has a winding shaft to wind a seat belt. A motive spring pretensions the winding shaft in the winding direction of the seat belt. An electric motor provides a torque that can be transmitted to the motive spring to change the spring force. A switch coupling transmits the torque of the electric motor drive to the winding shaft to retract the seat belt. To transmit the torque, a drive wheel, which is rotatably mounted on a shaft non-rotatably and coaxially connected to the winding shaft and which is non-rotatably connected to an outer spring end of the motive spring by a rigid rotational connection. A first active surface of the coupling is movably mounted against a restoring force to a component that is securely connected to the rigid rotational connection and rotatable around the shaft. A second active surface of the coupling is non-rotatably connected to the shaft.