To provide a structure capable of transmitting a bidirectional torque, namely, a structure capable of transmitting a strong torque, and giving high transmission efficiency and different change gear ratios according to the direction of the transmitted rotational motion.

A pair of friction roller type speed change units 30a, 30b capable of transmitting only a unidirectional torque respectively between a center roller 4a and an outer ring 15a and having mutually different change gear ratios are combined in the axial direction in the state where the directions of transmittable torques are mutually reversed between both members 4a, 15a. Each friction roller type speed change unit 30a, 30b is formed by including guide roller 10a, 10b and a wedge roller 11 respectively.