PURPOSE: To enable a stable combustion of an entire object to be ignited with a high productivity by a method wherein a conveyor is driven while the object to be ignited is positioned at the most-near position of an inlet part on a conveyor at the ignition part and kept at its complete ignited condition.

CONSTITUTION: Upper and lower thermometers 39 and 40 are arranged at the upper and lower two locations which are the most near location of an inlet part in a conveyor advancing direction at an ignition promoting part 29. The upper thermometer 39 is set at a substantial same level as that of a lower end of a lower porous plate 33 arranged at an ignition part 28, and the lower thermometer 40 is set at such a level as enabling an already-ignited object having a specified thickness in respect to the upper surface of the conveyor 24. In case of an initial operation of the combustion device 10, the item 11 to be ignited stayed at the ignition part 28 is ignited with an igniter means 37. After the ignition of the ignited object 11 at the upper porous plate 34 is confirmed, the conveyor 24 is intermittently driven and then the ignition part is moved to the ignition promoting part 29. After this operation, under a condition that the thermometers 39 and 40 detect a complete ignited condition of the ignited item 11, the conveyor 24 is driven.