Abstract: In the heat processing apparatus, a combustible gas evaporated from a liquefied gas tank is mixed with air and supplied from a gas mixture supply means to a combustion chamber, where the gas mixture is subjected to complete and flameless combustion through the catalyst, and the combustion heat is conducted to the iron tip for use in the heat processing of a work. A gas flow channel with a reduced flow resistance is formed continuously through out the catalyst for decreasing the pressure loss in the gas mixture. Further, ignition ports at the inlet of the combustion chamber are provided with a shutter mechanism for closing the ports after the completion of the ignition. The improved structure of the gas flow channel and the shutter co-operate to attain more effective and stable combustion in a compact structure of the apparatus.