To treat air containing dust generated when seasonings such as sugar and salt, food additives, and other granules are charged into a treatment tank in a beverage factory.

Air containing dust and steam generated in a treatment tank is first introduced into cyclone dust collecting chamber 52 by sucking with an ejector 88, condensed water is produced by a negative pressure and cooling, the condensed water is stuck on the inner wall of the chamber 52, and the dust is collected. The treated air is purified further by a filter element 72. The lid 68 of the chamber 52 is opened as required, and the inner wall of the chamber 52 is washed with water so that sugar and others adherent to the inner wall of the chamber 52 can be washed off easily.