Disclosed is a power transmission device that disconnectably transmits a torque between a first rotary member and a second rotary member that are each rotatable about a shaft, said power transmission device comprising: a clutch that disconnectably and drivably connects said first rotary member and said second rotary member; a motor including a rotor that is rotatable about said shaft; an input member that is rotatable about said shaft by being connected to said rotor, and that has an eccentric shaft that is eccentric to said shaft; a fixed member that is immovable about said shaft; an intermediate member that undergoes eccentric movement by fitting with said eccentric shaft, and that causes rotary movement about said eccentric shaft by meshing with said fixed member; an output member that is rotatable about said shaft, and that follows said intermediate member by engaging therewith; and a cam mechanism that is interposed between said output member and said clutch, and that converts the rotary movement of said output member into movement in the direction of said shaft and presses said clutch.