PURPOSE: To predict breakage of the wall of a container wherein a waste is thermally liquefied in the absence of air and to thereby prevent the explosion due to contact of a combustible gas with air by using. As the container, one having a specified structure.

CONSTITUTION: A waste (e.g. a waste tire) is liquefied by heating the waste in the absence of air in a waste container which comprises an outer wall 5 which faces a combustion side 6, an inner wall 7 which is installed inside the outer wall 5 in such a manner as to be out of contact with the outer wall 5 and which contains the waste, and pref. a pressure-detecting device 14 which detects the pressure of a fluid existing in the space between the outer wall 5 and the inner wall 7 and thus detects the breakage of the inner wall 7 or the outer wall 5 from the change in pressure of the fluid.