A power system includes an electric motor, a transmission, and a differential gear system. The transmission includes a first gear that is mechanically connected to the electric motor, a second gear that has a rotation axis in common with the first gear and is mechanically connected to a differential gear casing of the differential gear system, a pinion gear that meshes with the first gear and the second gear, and a pinion holder that rotatably supports the pinion gear. The pinion holder has a pinion gear supporting portion which is disposed on a side of the differential gear casing of the differential gear system to support the pinion gear, relative to a meshing portion between the second gear and the pinion gear. An inner diameter of the second gear at the meshing portion is equal to or smaller than an outer diameter of the pinion holder.