A wheel drive unit includes a planetary gear mechanism including a planetary gear and an internally-toothed gear. A casing is integrated with the internally-toothed gear, a wheel is attached to the casing, and the casing transmits rotation of the internally-toothed gear to the wheel. A bearing is fitted to an inner circumferential surface of the casing at a position more toward an interior of a vehicle than the planetary gear and rotatably supports the casing. An inner diameter of an outer race of the bearing is larger than an outer diameter of the planetary gear.