PURPOSE: To facilitate the control of a fluid incinerator, and to decrease the generation of NOx being accompanied by the incineration of sludge, by supplying a feeder for a fixed quantity of sludge when incinerating sludge containing an ammonia compound in the fluid incinerator.

CONSTITUTION: Sludge in a storage tank 1 is fed into a sludge hopper 3 by means of a screw feeder 2. Sludge is discharged in a fixed quantity condition by disposing a rotary feeder 4 into the sludge hopper 3 as a fixed quantity feeder. The feed capacity of a fixed quantity of sludge is further promoted by mounting not less than one flow-rate control plates 5 produced by installing a plurality of passing holes 5a to a plate body to a sludge discharge portion of said hopper 3. Sludge passing through the flow-rate control plates 5 is sent to a sludge incinerator 7, a turning fluid-layer furnace, by means of a snake conveyor 6, and agitated by a fluid layer 14 heated by means of a starting burner 8 and auxiliary combustion burners 9 in the inside and burnt.