PURPOSE: For preventing noise, to give a sufficient space to a cabinet serving as silencing chamber also on suction side so that both high-and low-frequency sounds may be silenced and to obstruct the transmission of vibration to discharge piping by means of a flexible joint.

CONSTITUTION: High-frequency sound is sucked by a sound absorbing material 2 while the air sucked in an upper chamber 1d from the lower peripheral edge of a hook 4 through an inclined opening 1b upon the start of operation. Thereafter, low- frequency sound is cancelled when said air flows in a lower chamber 1e while throttled by a small-diameter pipe 3. Next, the vibration generated by a blower 6 is absorbed by a flexible tube 10 while said air having come out of the suction hole of a blower 6 through a communicating pipe 8 after expanding at said lower chamber 1e and passing the peripheral portion of a motor 7 flows into a discharge piping 14 through a flexible tube 10. Noise can be completely silenced since said vibratin is absorbed by a buffer material also.