PURPOSE: To minimize noise leakage to the outside of a motor by installing a suction duct which leads outside air to a suction port, and a discharge duct which passes compressed air from a discharge port so as to cover the easing of the motor.

CONSTITUTION: By providing a suction port 15 at the easing 3a of a brush motor 3, and a discharge port 7 at the casing 1a of a centrifugal pump 1 respectively, an air passage 17 which passes the mounting position of a brush 12 is formed in the easing 3a of the motor 3. It is thus possible to cool the brush 12 by the outside air which runs through an air passage 17 and restrain temperature from rising due to its friction. As a result, it is also possible to minimize wear to the brush 12 and prolong the service life of the motor 3, that is, a motor pump.