PURPOSE: To improve durability of a cylindrical part and attain downsizing by reducing concentration of stress in the root part of the cylindrical part even if a bending moment is generated in a differential case by the radial force of differential gear supported in a cantilever form.

CONSTITUTION: A differential case 5 is supported through a pair of right and left bearings 3, 4, in an axial case 2, and a differential gear 6 is mounted on a cylindrical part 5B protruding to one end from the main part 5A of the case 5. The bearing on the side of the gear 6 supports the gear 6 so that the cylindrical part 5B of the case 5 fitted therein is supported.