A mounting structure for a speed reduction device of a vehicle includes a vehicle frame, a casing mounted on the vehicle frame at a casing mounting portion, a brake caliper mounted to the casing at a caliper mounting portion, a brake disc mounted on a drive axle of the vehicle, and a clamping portion mounted on the brake caliper for applying clamping force to the brake disc. The clamping portion, the caliper mounting portion, and the casing mounting portion are positioned on a substantially straight line, and are positioned substantially parallel to the direction of braking force.