To prevent fluid from evaporating, drying and solidifying in piping in a waste treating furnace and prevent residues from clogging to the inside of a tube, by providing a double pipe through a furnace shell of the furnace body and providing an injection port for a cooling medium to an outer tube as well as providing an injection port for volatile fluid and an injection port for compressed air to an inner tube.

When waste is combusted in a rotary kiln wherein the waste is fed through a hopper, uncombusted gas and residues are generated. The uncombusted gas flows into a secondary combustion chamber which is disposed at an entrance side of a stoker furnace, and the residues are discharged onto a fire grate at the entrance side of the stoker furnace and combusted thereon. A blowing device 1 is set at a position other than a waste feeding port of the rotary kiln furnace, passing through a furnace shell of the furnace body. The blowing device 1 is constituted with a double tube having an inner and an outer tubes 2, 3, the inner tube 2 being provided with a low volatile fluid injection port 4 and a compressed air injection port 5. Further, the outer tube 3 is provided with a cooling medium injection port 6, so that the low volatile fluid can be supplied to the furnace without causing clogging.