To prevent the deposition and accumulation of dust, etc., in a thermal decomposition gas duct for introducing a thermal decomposition gas generated in a dry-distillation thermal decomposition drum to a fusion combustion apparatus, to thereby prevent the duct from being blocked.

This cleaning apparatus 26 is installed in a thermal decomposition gas duct 6 for introducing a thermal decomposition gas G generated in a dry-distillation thermal decomposition drum 3 for dry distilling and thermally decomposing a waste W to a fusion combustion apparatus 7 and removes deposits accumulated in the gas duct 6. The gas duct 6 is composed of vertical sections 6a and 6c and a horizontal section 6b. The vertical sections 6a and 6c are equipped with sweeping apparatuses 27 for sweeping deposits accumulated on the inner surfaces of the sections 6a and 6c; and the horizontal section 6b is equipped with a transport apparatus 28 for transporting deposits accumulated in the section 6b to the fusion combustion apparatus 7.