Disclosed are a combination of a drive power transmission device and a differential gear, which combination is decreased in the number of parts, increased in rigidity and reduced in weight as well as in manufacturing cost, and a method of manufacturing the combination. A gear shaft which is provided with a drive gear for a differential gear is rotatably supported in a differential case. The differential case is provided with a partition wall portion which extends outwardly from an opening end portion thereof from which the gear shaft protrudes. A clutch case is secured to the circumferential edge portion of the partition wall portion thereby to define a housing chamber. A housing with a clutch receiving chamber formed therein is rotatably supported on the clutch case inside the housing chamber. In the clutch receiving chamber, outer clutch plates are engaged at outer circumferential portions thereof with the internal surface of the housing to be bodily rotatably but axially movable relative thereto, while inner clutch plates arranged in an alternate fashion with the outer clutch plates are engaged at internal surface portions thereof with an engaging portion of the gear shaft to be bodily rotatable but axially movable relative thereto. Thus, the inner clutch plates are drivingly connected directly with the gear shaft without using any inner shaft which would otherwise be necessary to support the inner clutch plates bodily rotatably and axially movably relative thereto in the housing.