PURPOSE: To separate and sort products made of specific plastic materials having nearly same densities but different chemical compositions by purposes by individually carrying the product and irradiating the products with electromagnetic radiations, and then, measuring the electromagnetic radiation absorbancy of the products.

CONSTITUTION: For a polyolefin or polyester resin and a halogenated resin having high electromagnetic radiation absorption coefficient, such products as containers, plates, etc., having an average thickness of 0.05-5mm are carried to an irradiating zone on a conveyor belt and the products are irradiated with electromagnetic radiations. The electromagnetic radiations are obtained from a radioactive material which radiates 1-3,000 watts of X rays having a wavelength of 0.1×10-8 to 4.75×10-8cm in the air and 40×10-9 to 70×10-8cm in a vacuum or gamma rays of ≥103 becquerels. An electromechanical system which detects the intensity of the transmitted electromagnetic radiations with a scintillation counter, etc., and separates the products by purposes based on the intensity detected by means of a threshold comparator is used.