A power transmission device including a planetary gear, a differential gear and a differential case. The planetary gear includes a carrier, and pinion gears supported by pinion shafts. The differential gear includes a pair of bevel gears supported by a bevel gear shaft, and side gears engaged with the bevel gears. The carrier defines pinion shaft insertion holes in which pinion shafts are respectively inserted. The differential case defines bevel gear shaft insertion holes in which the bevel gear shaft is inserted. A straight line that penetrates the bevel gear shaft insertion holes overlaps with the pinion shaft insertion holes in a circumferential direction, and the bevel gear shaft passes through a center of a circle that connects the pinion shaft insertion holes. When viewed along an axial direction, the pinion shafts do not overlap the side gears, with the side gears being arranged radially inwardly than the pinion shafts.