PURPOSE: To miniaturize equipment wherein a resistance heating element comprising two kinds of granular materials melts ashes stacked thereon with its sufficient self-heat generation and forms dropping flow passages among the granular materials to drop molten ashes therethrough, and gas evolved at the time of melting the ashes is thermally decomposed completely with heating element.

CONSTITUTION: A resistance heating element 32 comprising a granular mixture of a graphite-granular material with a silicon carbide-granular material is packed between secondary electrodes 28 opposed to each other, and the top of the resistance heating element 32 is formed into a substantially flat face on which ashes A to be disposed of are stacked. A heating part 33 for the ashes A is formed by the contact face of the resistance heating element 32 with the ashes A. In this case, the grain sizes of the graphite-granular material and silicon carbide-granular material are 5 to 10mm, respectively, and a volumetric mixing ratio is 4 to 1 or 5 to l. Accordingly, gaps among the granular materials forming the resistance heating element are wide, and flow passages enough to allow molten ashes to drop therethrough are formed. Moreover, such flow passages are formed in a mesh shape throughout the entire part of the resistance heating element 32.