Abstract: A rotating electrical machine includes, a cooling circuit 4 is provided for introducing oil to inside a housing, for cooling an inner periphery and outer periphery of a slotless stator in that order. Moreover, there is also provided a cover plate for preventing back flow of the oil introduced to inside the housings, to an outer peripheral side of the slotless stator 1. As a result, oil which has just been introduced to the housing, and has not yet been supplied for cooling the heat source, is promptly circulated to the inner peripheral side of the stator which requires much more cooling, so that the temperature rise of the overall rotating electrical machine is effectively suppressed. Moreover, a part of the oil introduced to inside the housing is used for lubricating bearings supporting a rotor.