Abstract: A low-cost volume-reducing treatment method for waste which thermally decomposes or burns chlorine-containing waste while the generation of hydrogen chloride and dioxin is completely or considerably suppressed. According to the method, volume of the waste can be greatly reduced. Shredder dust and other waste which contains chlorine derived from, for example, chlorine-containing polymers is thermally decomposed or burned at a temperature of 300.degree. to 1000.degree. C. in a reducing atmosphere where unburned carbon remains. Preferably, a basic material like red mud which contains alkali metal oxides or alkaline earth metal oxides is added before treatment.