To provide a structure capable of reducing a friction loss in a part in which inclined surfaces with a bus line shape inclined with respect to the center of rotation are brought into rolling contact with each other, because contact pressure has to be increased by a pressing device.

Loading cam devices 15b and 15b being the pressing devices are provided on the side of an annular roller 13b. A distance from the center of rotation of the annular roller 13b to a traction part associated with an inclined bus line shape can be increased, and a difference between peripheral speeds at both ends of each traction part can be decreased. Consequently, the above problem can be solved by keeping a friction loss in each traction part small.