To solve a problem that when treated ash remained after the incineration treatment of wastes and having toxic materials of halogen-containing substance (especially chlorine-containing substance) is used as a resource through melting and vitrification, there is a danger of deposition of toxic materials during the heat treatment when the treated ash is molten and vitrified.

The treated ash having halogen-containing substances and a treating agent for dechlorination which contains glass components, are charged into a heat treatment furnace 1, and they are heat-treated. This can perform simultaneously dechlorination and vitrification to obtain glass products.