In a positive torsion angle region in which a torque is transmitted from an engine side, a small hysteresis torque is generated at all times. Therefore, torsional vibrations of a small amplitude occurring during idle operation can be effectively attenuated by the small hysteresis torque, without switching to a large hysteresis torque, for example, during idle operation of the engine. As a result, the driver can be prevented from feeling uncomfortable due to switching to a large hysteresis torque during idle operation, and drivability can therefore be improved.