To provide a power transmission device capable of improving fuel consumption by arranging a one-way clutch between a power source and a transmission in parallel with an input device.

In the power transmission device including the input devices 4, 12 for transmitting torque output by the power source 2 to the transmission 5, the one-way clutch 15 provided in parallel with the input devices 4, 12, which is capable of transmitting the torque from the transmission 5 to the power source 2, but incapable of transmitting the torque from the power source 2 to the transmission 5.