Abstract: An apparatus for converting synthetic resin into oil thermally decomposes the synthetic resin by heating it in a heating vessel, thereby producing oil. The apparatus includes the heating vessel and a heating furnace. The synthetic resin fed into the heating vessel is stirred. At least the lower part of the heating vessel is disposed in the heating furnace. By providing a radiating fin on the outer surface of the upper part of the heating vessel disposed outside the heating furnace or providing a heat-insulation on the outer surface of the upper part of the heating vessel disposed in the heating furnace, the temperature rise in the upper part of the heating vessel is limited.