PURPOSE: To utilize the most of combustion energy of formation gas generated in a formation gas generating chamber of thermal decomposition treatment facilities.

CONSTITUTION: Combustible industrial waste 10 such as waste tire is charged from a charging port 12 of a thermal decomposition treatment facilities main body 2 into a formation gas generating chamber 7 to be ignited by a burner. The formation gas generating chamber 7 is sealed after ignition to control a formation gas generating blower 11 for sending a proper amount of air into the chamber 7. The combustible formation gas generated in the chamber 7 is mixed with air by negative pressure in a carburetor 30 as a piston of an engine 40 is lowered to be sucked as a mixture into a cylinder of the engine 40. The engine 40 compresses the combustible formation gas mixed with air by the piston to explode the compressed gas by an ignition plug. A turning force is given to a crankshaft by a force generated by the explosion of the combustible formation gas to push down the piston.