PURPOSE: To enable the length of a noise reduction material to be changed easily in response to various required noise values by interposing a cylindrical intermediate body filled with an auxiliary noise reduction material between the pipe opening end and the pipe coupler of an air blower.

CONSTITUTION: A cylindrical pipe opening 4 for ejecting and a cylindrical pipe opening 5 for sucking are formed integratedly with aluminium alloy in a casing 2, and a noise reduction material 6 provided with an hollow space part 6a serving as the fluid passage of an air blower is mounted inside the pipe openings 4, 5. A cylindrical intermediate body 11 filled with an auxiliary noise reduction material 10 is interposed between the pipe opening ends 4a, 5a and a pipe coupler 8. The pipe openings 4, 5 are communicated with the hollow space part 6a of the noise reduction material 6, through the hollow space part 10a of the auxiliary noise reduction material 10. It is thus possible to respond easily to the various requirements of low noise level by adding and installing the intermediate body provided with the auxiliary noise reduction material or changing the length of the noise reduction material even if the air blower is a standardized commodity.