To transmit large motive power while holding durability by forming at least one surface of the driving surface and the driven surface as the curved surface having curvature in the shaft direction of the surface, and forming the contact part of the driving surface and driven surface in a straight line shape.

At least one surface of the outer peripheral surface 7a, 7a of power rollers 7, 7, the input side recessed surface 2a of an input side disc 2 and the output side recessed surface 4a of an output side disc 4 is formed as the curved surface having curvature in the shaft direction of the surface. These curvatures are desirably changed to adjust contact surface pressure in the contact part of the driving surface and the driven surface to maximize a traction factor expressed in the ratio of driving force transmitted to a driven side member from a driving side member to pressing force acting in the vertical direction on the contact part. Thus, large motive power can be transmitted while restraining reduction in the rolling fatigue service life.