To prevent excessive slide in a rotary power transmission device transmitting torque between an input shaft and a driven shaft through a roller.

This is a rotary power transmission device in which rollers for torque transmission 12, 15 are arranged between an input shaft 4 and a driven shaft 8 to transmit torque between the input shaft 4 and the driven shaft 8 through the rollers 12, 15. Second torque transmission paths 24, 27, 26 including a joint transmitting torque by utilizing the viscosity of fluid 23 are provided in parallel with torque transmission paths by the rollers 12, 15 and between the input shaft 4 and the driven shaft 8.