PURPOSE: To improve the noise reduction function, and simplify the structure by surrounding a pump main frame with a suction noise reduction chamber part and a discharge noise reduction chamber part, and communicating a communication port with a lead-in port, and communicating a lead-out port with a receiving port.

CONSTITUTION: A case 2 for surrounding a pump main frame 1 is divided into a suction noise reduction chamber part 3 and a discharge noise reduction chamber part 4, and a suction port 5 communicated with the outside is formed in the suction noise reduction chamber part 3. A communication port 7 communicated with a lead-in port 6 of the main frame 1 is formed, and a receiving port 9 communicated with a lead-out port 8 of the main frame 1 is formed in the discharge noise reduction camber part 4. A discharge port 10 for discharging the pressure gas from the main frame 1 to the outside is formed, and the main frame 1 is surrounded by the suction noise reduction chamber part 3 and the discharge noise reduction chamber part 4, and the communication port 7 is communicated with the lead-in port 6, and the lead-out port 8 is communicated with the receiving port 9. The noise reduction function is improved, while the case 2 also works as a noise reduction chamber, and the function is simplified, and a device is made compact without forming a case 2 large and forming a noise reduction chamber separately by dividing the case 2 into the suction noise reduction chamber 3 and the discharge noise reduction chamber 4 and surrounding the main frame 1 with these noise reduction chambers 3, 4.