which a cooling medium flows and the cooling medium which is increased in pressure by a fan 23 for flowing of the cooling medium goes through a rotor 7 and an air gap 24 to cool a stator core 4 and an armature winding 6 in exhaust sections 26 which are positioned at an axial end region and in a axially central region to be exhausted through cooling ducts not shown or to be circulated again into the path through a heat exchanger at this time a part of the cooling medium which is increased in pressure by the fan 23 cools the armature winding 6 then goes through a cooling medium flowing path 25 to cool the stator core 4 and the armature winding 6 in an intake section 27 in which a cooling medium in the machine is caused to flow radially inwardly of the cooling ducts from radially outwardly thereof in an opposite manner to the exhaust section then joins a cooling medium which flows through the rotor 7 and the air gap 24 in the air gap 24 and is exhausted through cooling ducts not shown in the exhaust sections 26 or circulated again into the path through a heat exchanger fig5 shows a structure of the stator core in the third.