To provide a power transmission device by which fluctuation of revolution transmitted to driven side equipment can be effectively decreased without setting the spring constant of an elastic member in response to the kind of power source.

A contact member 50 is detachably fit to a pulley 10 and brought into contact with a hub 43 of a torque limiter mechanism 40 at a prescribed contact-pressure. The resonance frequency depending upon the spring constant of a buffer rubber 40 can be adjusted according to attachment/detachment of the contact member 50 or magnitude of the contact pressure. Thus, even when the specific frequency range wherein fluctuation of the revolution is increased according to the kind of engine, the fluctuation of revolution transmitted from the engine to a compressor 1 can be effectively decreased without setting spring constant of the rubber 30 in response to the kind of the engine.