The transmission case is provided with a bearing portion having a through hole in which a power transmission shaft is inserted, a fitting portion having a mating surface on which another member is superimposed, a plurality of fastening portions provided in the fitting portion, and ribs provided between the bearing portion and the fastening portions, respectively. The ribs are arranged between the bearing portion and the fastening portions, respectively, the fastening portions being other than the fastening portion that is the closest to the bearing portion amongst the plurality of fastening portions.