The present invention provides a power transmission device where inspection and adjustment of an electric motor connected to the input shaft and output shaft of the device are facilitated. In the power transmission device, the rotor (13) of the electric motor (2) is placed between a first shaft (27) on the input side and a second shaft (7) on the output side, and the first shaft (27), the second shaft (7), and the rotor (13) are integrally connected to each other at least in the rotation direction. The first shaft (27) is connected to the rotor (13) and the second shaft (7) is connected to the first shaft (27).