PURPOSE: To remarkably reduce the rising time of a batch carburization furnace after blowing of RX gas (CO-H2-N2 gas) by cooling the furnace to a specified temp. after operations are finished, introducing gaseous N2 and external air into the furnace, and finishing burnout when the CO concn. is diminished to zero.

CONSTITUTION: The batch carburization furnace 1 is stopped, the supply of RX gas is stopped, and the furnace temp. is lowered from 930°C to 850°C. Gaseous N2 is introduced into the furnace 1, an outlet door 4 is opened to burn the RX gas remaing in a combustion chamber 7, and the door 4 is closed. Meanwhile, the gas in the carburization chamber 6 is diluted with gaseous N2, external air is introduced 14 when the CO concn. in the chamber atmosphere is decreased lower than the lower limit, and the suspended carbon in the furnace is burned and gasified by the gaseous mixture of N2 and air. The burnout is finished when the CO2 concn. in the furnace transiently increased begins to decrease or the CO concn. is diminished to zero, and the supply of air is stopped. After that, gaseous N2 is continuously supplied 15 into the chamber 6 so that the furnace pressure is not decreased to zero or vacuum, and the oxidation in the furnace and intrusion of air into the insulating material are prevented.