To provide a waste classifying apparatus capable of preventing operation troubles caused by the clogging of a conveyance duct.

Light-gravity materials, dust and exhaust gas discharged from a discharge port 7b of a rotary impacting apparatus 7 are transferred through a main conveyance duct 12 into a cyclone 8 via a feeding port 8a of the cyclone 8. Therein, a bore diameter of the main conveyance duct 12 is larger than bore diameters of sub conveyance ducts 13, 14, 15 and is 1.2 times or more the bore diameter of the sub conveyance duct 13, and the main conveyance duct 12 is constituted so as to form an inverted L shape by connecting a vertical duct 12a and a horizontal duct 12b on a bend part 12c. Therein, the length of the horizontal duct 12b is set to be short, at the same time, the flow rate in the main conveyance duct 12 by means of a suction blower 10 is controlled within a specified flow rate region (low flow rate suction conveyance operation). Therefore, particulate matter in the light-gravity materials is hardly transferred and the clogging of the main conveyance duct 12 due to the particulate matter is hardly caused.