A direction in which cooling air generated by a cooling fan flows to be discharged is perpendicular or nearly perpendicular to a direction in which diffusers are inclined. Thus, airflow resistance is increased by the diffusers, and the cooling air cannot be efficiently discharged from discharge ports provided circumferentially in an outer peripheral portion of a housing. Further, a stator coil cannot be sufficiently cooled. An electrical rotating machine includes: a rotor having a cooling fan on an end face of the rotor; a stator that is arranged opposite the rotor and has a stator coil with a rotation clearance provided between the stator and the rotor; a housing that holds the rotor and the stator; a plurality of intake ports that are provided in a side wall portion of the housing; a plurality of discharge ports that are provided circumferentially in an outer peripheral portion of the housing; and a plurality of diffusers that are provided circumferentially on an inner wall surface of a corner portion of the housing, the diffusers inclining toward the side opposite to a rotational direction of the rotor.