Belt retractor comprising - a belt shaft which is rotatably mounted in a housing and onto which a seat belt can be wound, the housing being able to be fastened to the vehicle, and - an electric motor for driving the belt shaft to move rotationally, and - a gear mechanism which transmits the rotational movement from the electric motor to the belt shaft, - the gear mechanism being able to be driven in a first force-transmission path as an assembly to drive the belt shaft with a first torque, and - the gear mechanism being able to be driven to drive the belt shaft with a second torque, by shifting a speed-controlled and/or torque-controlled coupling, whereby a second force-transmission path is opened, - the coupling having at least one coupling element which is springloaded by a spring into engagement in a first part of the gear mechanism, - a drive wheel which is connected to the electric motor for conjoint rotation and has a polygonal force-transmission profile being provided, and - the coupling element having at least one force-transmission portion (20,21) which abuts the polygonal force-transmission profile and by which the coupling element can be moved, against the force of the spring, out of engagement in the first part of the gear mechanism due to a relative movement of the drive wheel relative to the coupling element when a predetermined rotational speed transmitted by the drive wheel and/or a predetermined torque and/or a predetermined rotational acceleration is exceeded, and - the coupling element being mounted on a second part of the gear mechanism, and - the second part having a gear wheel connected for conjoint rotation, with which it is in toothed engagement with one or more gear wheels of a transmission gear mechanism, characterized in that - the spring is formed by a bow spring which is connected with a first end to the coupling element and with a second end to the second part. - a belt shaft which is rotatably mounted in a housing and onto which a seat belt can be wound, the housing being able to be fastened to the vehicle, and - an electric motor for driving the belt shaft to move rotationally, and - a gear mechanism which transmits the rotational movement from the electric motor to the belt shaft, - the gear mechanism being able to be driven in a first force-transmission path as an assembly to drive the belt shaft with a first torque, and - the gear mechanism being able to be driven to drive the belt shaft with a second torque, by shifting a speed-controlled and/or torque-controlled coupling, whereby a second force-transmission path is opened, - the coupling having at least one coupling element which is springloaded by a spring into engagement in a first part of the gear mechanism, - a drive wheel which is connected to the electric motor for conjoint rotation and has a polygonal force-transmission profile being provided, and - the coupling element having at least one force-transmission portion (20,21) which abuts the polygonal force-transmission profile and by which the coupling element can be moved, against the force of the spring, out of engagement in the first part of the gear mechanism due to a relative movement of the drive wheel relative to the coupling element when a predetermined rotational speed transmitted by the drive wheel and/or a predetermined torque and/or a predetermined rotational acceleration is exceeded, and - the coupling element being mounted on a second part of the gear mechanism, and - the second part having a gear wheel connected for conjoint rotation, with which it is in toothed engagement with one or more gear wheels of a transmission gear mechanism, characterized in that - the spring is formed by a bow spring which is connected with a first end to the coupling element and with a second end to the second part.