Abstract: In the continuous carburization furnace in which the temperature of the heaters can be controlled individually at every carburization processing position; carburization reference data at each carburization processing position is read; a temperature and carbon potential at each position at least during carburization and diffusion processes is detected; a carburized quantity of the processed member at each position is calculated with reference to the detected temperature and carbon potential; a carburization history is calculated by integrating the carburized quantity at each position of the carburization processed member, and a carburizing condition at a next carburization processing position is determined depending on a difference between the carburization history at the time of terminating the carburization process at each position of the carburization processed member and the carburization reference data at each position.