To realize the reduction of weight of a power transmission device by overcoming a drawback that an excessively large rotational torque is transmitted to a power transmission path and to sufficiently suppress the generation of a change of a rotational speed by overcoming a drawback that phases between one universal joint and another universal joint are displaced from each other. A damper mechanism is provide in the course of a power transmission path from an engine to a final reduction gear. The damper mechanism transmits a torque from the engine until the torque arrives at a predetermined value and prevents the transmission of a torque that exceeds the predetermined value.