PURPOSE: To enable the heat treatment of a steel wire having stable mechanical characteristics by predicting the steel wire temps. of every treating zone, automatically plotting the results thereof and visually displaying the predicted temps. in correspondence to each of the heating zones.

CONSTITUTION: The steel wire and a wire having a circular sectional shape are continuously heat-treated. The number of the zones of a heating furnace, the atm. temps. of the respective zones, heating medium, the lengths of the respective zones, wire passing speed, and the wire diameter and thermal conductivity of the material to be heat-treated are inputted in such a case. The temps. of the steel wire in each of the heat treating zones of the steel wire to be heat-treated are predicted in such a manner. The results thereof are automatically plotted on an automatically formed equipment outline diagram and the predicted temps. of the steel wire to be heat-treated are visually displayed in correspondence to each of the respective heat treating zones to predict the temps. of the steel wire at the time of the continuous heat treatment. As a result, the steel wire temps. at the time of executing the heat treatments, such as lead patenting and fluidized bed patenting are predicted.