PURPOSE: To provide a new processing system which makes it possible to sort and separate a waste material into a styrenic component and a non-styrenic component without spending much labor and convert the styrenic component into a hydrocarbon oil efficiently and economically without a volume reduction.

CONSTITUTION: The system comprises the steps of: mixing a waste material containing an expanded styrene resin with a solvent for the resin to selectively dissolve and extract the resin in the waste material; heating, vaporizing and thermally decomposing the extract; cooling and liquefying the vaporized material to convert it into a hydrocarbon oil; and dissolving a part of the hydrocarbon oil to send it back to the extraction step.