A power transmission mechanism, wherein power transmission arms (42) deform elastically by receiving a force based on a transmission torque in a power transmission between a pulley (32) on an engine (E) side and a pivotally supporting member (35) on a compressor side so as to allow the postures of engaging recessed parts (43) to be varied relative to the pivotally supporting member (35), whereby the pulley (32) and pivotally supporting member (35) can be rotated relative to each other within a specified range of angle, following a sliding of rollers (39) due to the contact rotation thereof in the engaging recessed parts (43).