In a method of manufacturing a differential device, a hub of a ring gear is press-fitted to a flange from a first bearing boss side, then a press-fit portion between the flange and the ring gear is equally divided into a plurality of divided regions arranged along a peripheral direction, and simultaneously the divided regions are welded. Accordingly, the press-fit portion between the flange and the ring gear can be efficiently welded while welding distortion of the ring gear is eliminated or reduced even in a case where work windows of a differential case cut into a side surface of the flange on the first bearing boss side to form recessed portions.