To enable force-feed air from a compressor to perform pneumatic feed and vacuum action to an auxiliary machinery by the switching operation of an opening and closing valve by providing a connecting pipe with a conduit pipe branching off in the middle portion thereof, and connecting the conduit pipe to an ejector for vacuum action through the opening and closing valve.

A suction pipe 16 having an opening and closing valve 15 is connected to a dust collecting tower 12, and further the tip of the suction pipe 16 is provided with a removable hose 16a. A solid matter C is sucked by the vacuum action of an ejector 10 by the drive of a compressor 2, a solid matter and dust are selected in the dust collecting tower 12, the solid matter C is collected in a tank, and on the other hand, air containing dust is passed through a tertiary catch 4b. The purified air is sucked by the ejector 10 through an intake pipe 14 to be sent to a quaternary catch 4a. That is, the compressed air of the compressor 2 is force-fed to an external apparatus by the switching operation of opening and closing valves 6, 6a or conducts the vacuum operation.