To provide a burnout method for a vacuum carburizing furnace by which a burnout is performed only by air as a means of applying the burnout to a heat insulating material, and also the finished time of the burnout can easily be determined by monitoring the finishing time of the burnout with a sensor or the like.

The temperature of a heating chamber 4 is set to 850 to 950°C, and the inside of the heating chamber 4 is evacuated with a vacuum pump 10. When the pressure in the heating chamber 4 reaches 5 to 40 Kpa with a manometer 16, the air is charged inside the heating chamber 4 to perform the burnout. When the pressure in the heating chamber 4 reaches 50 to 90 Kpa, the injection of the air is stopped and a stop valve 9 is opened to exhaust the air. Thereafter, when the pressure in the furnace reaches 5 to 40 Kpa, the air is again charged to perform the burnout repeatedly. In this case, the exhaust gas from the inside of the heating chamber is monitored, it is determined that the burnout is finished by confirming that the concentration of CO2 in the exhaust gas reduces, the concentration of O2 is increasing and the drop of the temperature inside the heat insulating material suddenly reduces.