PURPOSE: To obtain a dust collecting function as a scrubber by using a system in which a liquid layer is used as a fluidized layer, and the heat of waste gas introduced into the liquid layer is not only recovered effectively but also dust in the waste gas is separated in the liquid layer.

CONSTITUTION: Waste gas G introduced from an inlet 11 provided at the lower part is blown out to the lower part of the inside of the liquid L in a fluid liquid layer 10 by a nozzle 1. Whereupon, larger part of dust present in the waste gas G is separated in the liquid L and air bubbles F are formed. The waste gas G containing small amounts of dust is redistributed by an auxiliary distributor 2 provided above the waste gas inlet 11 and raised in the liquid L, during which period the waste gas G is heat-exchanged with the liquid L and dust is separated. Since the waste gas G coming out of the fluid liquid layer 10 to the upper part contains no dust but contains the mist of the liquid L, the mist is separated by the nozzle 9 for atomizing the liquid and mist separators 4 and 5, provided above the level of the liquid L of the fluid liquid layer 10 and discharged from a gas outlet 12.