PURPOSE: To prevent burning of windings, by providing a heat transfer passage for cooling the windings and a heat sensing element with the windings so that a motor is stopped by controlling a temperature sensing switch by the temperature sensitive element when a temperature of the windings is further increased by an abnormal load.

CONSTITUTION: Fixed portions 14a on which a stator 17 having windings 16 assembled therein is mounted are disposed at 4 positions and 2 positions of them are adjacent to a heat transfer passage 15 formed on a housing 14. The heat transfer passage 15 is so constructed that it communicates with a pump room 20 and a portion of water pumped is introduced into it so that the stator 17 is cooled by water through a cooling unit 14a of the heat transfer passage 15. Temperature increase of the windings 16 is prevented due to a cooling effect of the heat transfer passage 15 and an accident of burning of a motor unit 10 can be prevented. In addition, a heat sensitive switch 71 such as a heat sensitive 70 is attached on the upper portion of the heat transfer passage 15 and then when a temperature of the windings 16 are increased furthermore the heat sensitive switch 71 is controlled by the heat sensitive element 70 to stop the rotation of the motor. With such an arrangement, burning of the windings 16 can be prevented in advance to increase reliability.