PURPOSE: To facilitate the machining of the storage holes of helical pinion gears and make the end faces of both helical side gears equal to the contact area of a differential case.

CONSTITUTION: A differential gear 7 is provided with a differential case 21 formed of plural case members 31, 33; helical pinion gears 55, 57 having gear parts 59, 61 enclosed in the storage holes 51, 53 of the case member 33 and meshed on one axial side, and gear parts 63, 65 connected to the gear parts 59, 61 through small diameter shaft parts 67, 69; helical side gears 37, 39 individually meshed with the gear parts 63, 65; and a collar part 73 formed at the case member 31 and opposed to the end face of a side gear 37.