To effectively recycle waste plastics separated from non-industrial waste or industrial waste, or the like, as a resource by a simple method and to utilize the waste plastics containing chlorine-containing plastics without removing the chlorine.

The waste plastics containing the chlorine-containing plastics and formed into granular state or small pieces is utilized as a reducing agent for non-ferrous metals when the non-ferrous metals containing heavy metals are fused or refined in a blast furnace or a refining furnace. Then, hydrogen chloride produced when the waste plastics is thermally decomposed in the blast furnace or the refining furnace is reacted with the heavy metals contained in the non-ferrous metals and fixed as the heavy metal chlorides.