PURPOSE: To reduce torsional vibration in a torque transmission system all over by providing a resonance control means for driving a frictional force variable means in a direction of increasing the frictional force when the generating area of torsional resonance is detected by a resonance detecting means.

CONSTITUTION: A frictional force variable means f for changing frictional force due to a frictional member d, a resonance detecting means g for detecting a torsional resonance phenomenon generated in a torque transmission system, and a resonance control means h for driving the frictional force variable means f in the direction of increasing the frictional force when the generating area of the torsional resonance is detected by the resonance detecting means g, are provided. Namely, when the resonance phenomenon is generated in the torque transmission system, the frictional force variable means f is driven to increase the frictional force by a frictional member d so as to increase hysteresis for damping the torsional vibration. Accordingly, the torsional vibration in the torque transmission system is effectively decreased and also, is a area where resonance phenomenon is not generated, the frictional force by the frictional member d is decreased for reducing torque change in the area.