PURPOSE: To prevent the lowering of dust collecting efficiency, by providing a means shaking down dust adhered to a traveling discharge electrode on the traveling way of said traveling discharge electrode.

CONSTITUTION: Dust containing gas is introduced into a casing 1 from two directions and each gas streams are mutually impinged at the central part of a chamber 15 to be uniformly separated to the left and right. During this time, dust is charged in the electric field formed by a discharge electrode 30 and a dust collecting electrode 12 to be collected by the inner surface of the belt like dust collecting electrode 12 during driving and the purified gas is exhausted from exhaust ports 4, 5. The dust collected by the dust collecting electrode 12 is compressed between rollers 8, 9 to be formed into a cake and this cake is scraped off by each scrapers to be discharged to the outside from a take-out pipe 55. When dust is adhered to the discharge electrode 30 to be thickened thereon and dust collecting efficiency is lowered, a motor 43 is driven to travel the discharge electrode 30 by the revolving force thereof and the adhered dust is shaken down by a dust removing means 33.