A differential case (23) is therein provided with a plurality of rotating discs (38) that are spline coupled to an outer peripheral side of a right side gear (35), and a plurality of non-rotating discs (39) that are arranged between the respective rotating discs (38). A pressure ring (43) is disposed between a right retainer (41) and the rotating disc (38). The right retainer (41) is provided with a piston (46) that applies a load to the pressure ring (43) to bring the rotating discs (38) and the non-rotating discs (39) into frictional contact. A lever member (53) is disposed between the differential case (23), the right side gear (35) and the pressure ring (43). The lever member (53) transmits a reaction force due to the engagement between the pinion gear (33) and the right side gear (35) to the pressure ring (43) to control a load to be applied to the pressure ring (43) from the piston (46).