Abstract: A plastic material with a paint film is coarse-crushed, and a film decomposition agent, e.g. a heterocyclic compound such as imidazole, a triazine compound such as benzoguanamine, a phenylendiamine compound such as N-phenyl -N'-isopropyl-p-phenylene diamine, is added to the coarse-crushed material. The mixture is then heated and kneaded to dissolve the paint film and uniformly spread the particles of the paint film in the plastic material. The physical properties and surface quality of the plastic material are substantially the same as those of the original material.