POWER TRANSMISSION DEVICE

A power transmission device includes a motor having a motor shaft, a transmission mechanism, a reduction gear, and a case member. The transmission mechanism is connected downstream of the motor. The transmission mechanism has a band brake, and an actuator. A reduction gear is arranged downstream of the transmission mechanism. The case member houses the motor, at least a part of the transmission mechanism, and the reduction gear. The case member has an outer circumference wall that surrounds an outer circumference with respect to a radial direction perpendicular to a rotation axis of the motor shaft, and a side wall that is linked to the outer circumference wall, and that extends outwardly in the radial direction from the outer circumference wall. The actuator is provided adjacent to the outer circumference wall, and adjacent to the side wall, the actuator overlapping with the band brake in the radial direction.