Patent ID: 8894539

Claim:
A wheel driving speed reducer comprising: a parallel shaft gear mechanism that includes a parallel shaft gear; a planetary gear mechanism that is provided on a rear stage of the parallel shaft gear mechanism and includes planetary gears and an internal gear with which the planetary gears internally mesh; and a casing that accommodates the parallel shaft gear mechanism and the planetary gear mechanism, wherein a tooth portion of the parallel shaft gear protrudes and extends into a gap, which is formed between the casing and the internal gear or a member integrated with the internal gear, in an axial direction, the tooth portion of the parallel shaft gear and the internal gear or the member integrated with the internal gear overlap each other when seen in a radial direction; a brake mechanism that brakes the rotation of a rotating member of the speed reducer, wherein one member of the brake mechanism is integrated with the internal gear, and the tooth portion of the parallel shaft gear and the one member of the brake mechanism overlap each other when seen in the radial direction.