PURPOSE: To blow filtered air from a supply opening as well as to prevent a noise from occurring in an effective manner by inflating an expandable and contractible baglike body equipped with both air inlet and exhaust ports and inhaling air into the inner part, then contracting it and exhausting the air.

CONSTITUTION: When a crank 12 is rotated by a motor, a lower end of a baglike body 9 pinned to the lower end of a rod 13 serves as a slider and moves up and down periodically and continuously, making it double as both expansion and contraction means for the baglike body 9. At an expansion process from contraction time in the baglike body 9, a lift valve 16 in an inlet port 15 is pushed up and opened, and simultaneously a lift valve 16 in an exhaust port 14 is depressed in the shape of being attracted and closed, so that air passing through an inlet port 3 and a prefilter 4 is charged in an inner part of this baglike body 9 from the inlet ports 15. Next, at the contracting process, the valve 16 in the inlet port 15 is closed, the valve 16 in the exhaust port 14 is opened instead, and inhaled air passes through a chamber 7, also passing through an HEPA filter 6, and it is thus filtered and blown out of a supply opening 5.