A power transmission unit (41a) includes a motor (70); and a transmission case (42a) to enclose an input shaft (72), an output shaft (60), and a gear mechanism (80) that transmits driving power between the input shaft (72) and the output shaft (60). A motor case (120) attached to the transmission case (42a) on a side opposite the gear mechanism (80) of the transmission case has a cylindrical shape whose cross section is constant throughout a direction orthogonal to an axial direction of the motor case, and the motor (70) is placed inside the motor case.