PURPOSE: To prevent abraded dust from entering into bearings and lengthen the service life of the bearings by forming an air blasting passage passing through a connecting part around the connecting part to connect an output shaft of a driving means to a rotary shaft of a rotary pump, and carrying out a pump operation while blasting air to the connecting part through the air blasting passage.

CONSTITUTION: An air blasting passage 18 leading to a discharge port 16 from a release port 14 is formed between a pump frame 5 and a motor frame 11 opposed to each other by passing through a circular space A formed around a connecting part to connect a rotary shaft 7 to an output shaft 8, and the circular space A is communicated with the release port 14 and the discharge port 16 through a groove part 13. Discharge air produced simultaneously with an operation of a vacuum pump 1 flows through the air blasting passage 18 from the release port 14 by opening a check valve 15, and is discharged into a motor 2 from the discharge port 16, and is exhausted outside of the motor 2 from an exhaust cylinder 17. Thereby, abraded dust produced in an engaging part can be prevented from entering into bearings, and the bearings 3 and 9 can be also cooled by means of the discharge air so that the service life of the bearings 3 and 9 can be lengthened.