PURPOSE: To efficiently utilize heat generated in only one combustion unit for efficient liquefaction, gasification, and reforming of waste plastic to thereby realize energy saving by a constitution wherein waste plastic is liquefied in a melting chamber, gasified in a thermal decomposition chamber, and reformed in a catalytic reaction chamber.

CONSTITUTION: A melting chamber 3 and a thermal decomposition chamber 4 are arranged side by side in a heating furnace 1. Waste plastic is fed through an inlet 7 into the melting chamber 3, which is hermetically sealed and in which the waste plastic is heated and liquefied by the heat of combustion from a combustor 2. A rising internal pressure is utilized to sent the liquefied waste plastic through connecting path 5 to the thermal decomposition chamber 4, where the liquefied waste plastic is thermally decomposed and gasified by the heat of combustion from the combustor 2. The gasified oil is introduced into a catalytic reaction chamber 6, where it is catalytically reacted and reformed. The gasified light oil thus obtained is passed through a riser 60 and introduced into a condenser outside the furnace 1, where it is liquefied and separated into oil and water.