To reliably support a power plant regardless of the power plant type by disposing a rotational member that allows vertical movement in the vehicle and rotation in the roll direction of the vehicle between one end of a rod and a frame and between the other end of the rod and the power frame, and regulates the rotation around the vertical axis of the vehicle.

A rotating member 10 on the power plant side is disposed between one end of a rod 12 on the power plant 3 side, which supports the power plant 3 with respect to a side rail 8, and the power plant 3. Further, a rotating member 11 on the side rail side is interposed between one end of the rod 12 on the side rail 8 side and the side rail 8. With this support device, rotation around the vertical axis of the vehicle of the power plant 3 is regulated by the rigidity of the rod 12, while movement in the vertical direction and rotation in the roll direction of the vehicle is permitted. As a result, the mounted power plant 3, regardless of the type, can be reliably supported and the negative influence with respect to cab vibration during idling of the engine can be controlled.