PURPOSE: To arbitrarily regulate the amount of residual austenite (rR) present in the carburized layer of a carburized steel by changing the carbon potential of the internal atmosphere of a furnace in accordance with data on the relation between the amount of rR and the amount of carbon intoduced by carburizing.

CONSTITUTION: Data on the relation between the amount of carbon introduced by carburizing and the amount of rR are formed. Carburizing is carried out while changing the carbon potential of the internal atmosphere of a furnace in ≥2 steps during the carburizing in accordance with the data and while changing the treatment time at the same time. Thus, a desired amount of rR is obtd. in the carburized layer having a desired depth.