To provide an oilifying apparatus that can recycle waste plastics on a practical scale, and permits estimation of a thermolysis treatment temperature, a pressure in an oven and the like to attain quantitative feed, and a method therefor.

The waste plastic-oilifying apparatus is separated into a melting apparatus and a vaporization apparatus, has a decomposition vessel with its bottom plate in a wavy shape to accelerate heat conduction and has a vaporization plate installed in the vaporization apparatus. Liquefied plastics are gasified on the vaporization plate and are brought into contact with a catalyst thereby causing cutting of chains to give recovered hydrocarbon oil. Separation of the melting apparatus 1 from the vaporization apparatus 3 permits control of the vaporized gas even in a very small amount to lower the inner pressure inside the vaporization apparatus. On liquefaction of plastic wastes, the temperature is controlled stepwise within the temperature range from ordinary temperature to around 500C.