PURPOSE: To reduce the energy loss in removing foreign materials, and improve the fuel consumption required for pyrolysis, the efficiency for removing the foreign materials and pyrolytic efficiency.

CONSTITUTION: This pyrolytic furnace is obtained by installing a pyrolytic vessel and a hollow vertical rotating shaft 9 having a lower part immersed in a plastic melt in the pyrolytic vessel and a notch at the bottom of the peripheral wall, arranging a foreign material suction pipe 18 in the vertical rotating shaft 9, further providing a vacuum pump capable of sucking the foreign materials together with the plastic melt in the pyrolytic vessel through the foreign material suction pipe 18, fixedly installing stirring blades 15, protruding outward in the radial direction and curved toward the outside in the radial direction to the front in the rotative direction of the vertical rotating shaft 9 in the peripheral wall thereof and providing the stirring blades 15 with the shape of a curve changing from the outer peripheral surface side of the peripheral wall of the vertical rotating shaft 9 as a starting point so as to slowly reduce the curvature toward the tips when viewed from a plane.