Wheel driving speed reducer

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.