A power transmission device includes a transmission mechanism configured to transmit power generated by an electric motor to an output shaft, to which power generated by an internal combustion engine is transmitted, via engaging sections of a plurality of rotating members, and the transmission mechanism has a play to the engaging sections along a rotating direction, the play being larger than a relative displacement amount between the rotating member on the internal combustion engine side and the rotating member on the electric motor side when a rotation variation phase difference between the internal combustion engine and the electric motor is maximum. Therefore, there can be provided the power transmission device capable of suppressing an occurrence of noise.