PURPOSE: To recover useful plastics suitable for reuse by separation from plastics wherein various kinds of plastics are mixed.

CONSTITUTION: Plastics wherein a plurality of materials of plastics are mixed are classified with a plastics classifier 12. The plastics classifier 12 is composed of a low temperature crushing mechanism and a water-using specific gravity mechanism. The low temperature crushing mechanism is equipped with a low temperature chamber 1203. Liquid nitrogen is jetted by evaporation to crush plastics by impaction by using an embrittling characteristic at low temperature. Selection to a certain extent by a size is executed. Though selection by specific gravity is further applied to a part of the selected plastics, a device for gravity concentration 1209 is filled with water, and the plastics are separated into floating plastics and settling plastics.