To provide a power transmission mechanism in which dispersion of cutoff torque is prevented and having excellent reliability and durability are exerted by keeping the friction coefficient constant between a plate spring and a bent recess against which the plate spring is pressed.

This power transmission mechanism has a pulley, a shaft arranged concentrically with the pulley, and a hub fixed on the shaft and comprises a pair of plate spring fixing parts for fixing ends of the plate spring on inner circumferential surface of the pulley, and the bent recess where the plate spring is pressed against outer circumferential surface of the hub, and power is transmitted from the pulley to the hub by bending the center part of the plate spring to be pressed against the bent recess. A different kind of surface layer from the plate spring and the bent recess is interposed between the plate spring and the bent recess of the hub.