A case of an electric rotating machine, includes: a cooling passage which is provided inside the case along a circumferential direction of the case and through which a cooling fluid is able to flow; a cooling fluid inlet and a cooling fluid outlet which communicate with the cooling passage; and a rib which is provided inside the cooling passage, connect a wall portion on an inside in a radial direction of the case and a wall portion on an outside in the radial direction of the cooling passage along the circumferential direction, are arranged to be separated from each other in an axial direction of the case, and partition the cooling passage into a plurality of cooling passages.