PURPOSE: To aim at compactification in size, by closing up the tip side of a sub-nozzle by a shielding wall, while setting up a silencer element at the outer circumferential side, and forming a compressed air discharge port in a body at the outer circumferential part of the sub-nozzle.

CONSTITUTION: Inside an air passage 2, there are provided with nozzles 5 and 6 for in creasing a flow velocity of the air introduced from a compressed air intake port 3. A circumference of the nozzle 6 is surrounded by a silencer element 7, and a shielding wall 10 is solidly attached to a cover body 8. Compressed air collides with the shielding wall 10 of the cover body 8 and, upon changing its direction largely, it passes through the silencer element 7 and discharged to the outside, so that a device is compactible in size as a whole.