A motor/generator ( 1 ) comprises a cylindrical stator core ( 5 ) facing the outer periphery of a rotor ( 3 ) on the inner side of a case ( 2 ). Base plates ( 8 ) constituted by an electrical insulation material are laminated on both ends of the stator core ( 5 ). A plurality of coils ( 7 ) are wound on the laminated body comprising the stator core ( 5 ) and the base plates ( 8 ). A cooling jacket ( 6 ) is attached to each of the base plate ( 8 ) using engagement members ( 6 F, 6 G, 8 D, 8 E, 10, 15 ) in order to envelope the projection of the coil ( 7 ). The end planks ( 2 B, 2 C) of the case ( 2 ) hold and press the cooling jacket ( 6 ) toward the stator core ( 5 ). Consequently, without forming a flange in order to fix the cooling jacket ( 6 ), the cooling jackets ( 6 ) are secured at a predetermined position within the case ( 2 ).