To provide a combustion furnace which completely burns gas containing deleterious substance and discharges the same to the outside of a system after making the same harmless.

A plurality of heat resistant pipes 1 are installed in an insulating wall 3 at the near center of the same, and a plurality of electric resistance heat generating bodies 2 are installed so as to surround the heat resistant pipes 1 while the heat resistant pipes 1 are filled with oxidizable refractory balls 11-13 having a plurality of different diameters. The heat resistant pipes 1 and the oxidizable refractory balls 11-13 are heated at all times to about 1700°C by the radiation heat of the electric resistance heat generating bodies 2. The deleterious gas, induced from an external incinerator, flows into the heat resistant pipes 1 and passes gaps among the plurality of balls while meandering. In this case, the deleterious gas absorbs heat by contacting with the balls and is heated to about 1700°C whereby contained deleterious substance is burnt completely together with air and is discharged to the outside of the system through an exhaust tower.