Wheel drive unit

A wheel drive unit (100) comprises: a planetary gear mechanism (10) including a planetary gear (24) and an internally-toothed gear (28); a casing (30) integrated with the internally-toothed gear (28), a wheel (48) being attached to the casing, and the casing (30) transmitting rotation of the internally-toothed gear to the wheel; a bearing (46) fitted to an inner circumferential surface of the casing (30) at a position more toward an interior of a vehicle than the planetary gear (24) and rotatably supporting the casing. An inner diameter of an outer race (46B) of the bearing (46) is larger than an outer diameter of the planetary gear (24).