Abstract: Exemplary embodiments of the present invention can be directed to producing high-density pellets by molding waste plastic and to producing high-strength coke by mixing the pellets with coal and dry-distilling the mixture in a coke oven. As feedstock is used waste plastic that contains polyethylene, polypropylene and polystyrene, which are plastics that soften at a low temperature, at a total rate of about 50% or greater. The waste plastic is molded using a molding method of extruding it from a nozzle of a screw-type stuffing machine. In the method of this invention, the waste plastic can be heated to about 180˜260° C. in the molding machine and gas in the molding machine is sucked out. By this operation, the polyethylene, polypropylene and/or polystyrene are made molten and the amount of gas in the plastic is reduced. The plastic in this state is compression-molded by extrusion from a nozzle of about 15˜60 mm diameter.