To reduce manufacturing costs by minimizing power consumption while maintaining torque transmission efficiency high, and reducing the number of part items and machining costs irrespective of the high or low level of torque transmitted from an electric power motor.

A driving shaft 12 is disposed to be eccentric from an outer ring 16, a diameter gap between the outer peripheral surface of the driving shaft 12 and the inner peripheral surface of the outer ring 16 is varied in a circumferential direction, and during friction transmission, following the rotation of the driving shaft 12, a wedge roller 13 is moved in the circumferential direction and in a smaller diameter gap to press the inner peripheral surface of the outer ring 16. The diameter of a guide roller 15 is set roughly equal to the maximum diameter gap interval, and the guide roller 15 is inhibited from moving in the circumferential direction without needing any support shafts for supporting the guide roller 15.