To constitute a transmission device with lightweight, compactness and at low costs by attaching an auxiliary transmission mechanism to the device.

This power transmission device comprises a transmission device 3 that outputs driving force of a motor from toroidal transmission mechanisms 7 and 9 through a countershaft 31 disposed in parallel to the transmission mechanisms 7 and 9, and a power distribution device 5 disposed coaxially with a countershaft 31 and distributing rotation inputted from one countershaft 31 to the shaft wheel side and the rear wheel side. An auxiliary transmission mechanism 41 is disposed between the terminal of the countershaft 31 and the power distribution device 5. The auxiliary transmission mechanism is characterized in that it has a neutral position and a Hi-Lo switch mechanism.