A seat belt retractor for a vehicle with a rotatably mounted belt reel on which a seat belt can be wound and unwound has a biased motive spring that acts on the belt reel to produce a pulling force which acts on the seat belt, and during winding and unwinding follows a characteristic curve which is dependent on the extracted length of belt webbing. An electric motor drive adjusts the bias of the motive spring in such a way that the pulling force follows a characteristic curve corresponding to room temperature, which is approximately 20° C., at any temperature.