PURPOSE: To control the temps. in a heating furnace consisting of a preheating zone, a heating zone, and a soaking zone to prescribed temps. irrespectively of the fluctuations in the sizes of ingots in the stage of heating the ingots in said heating furnace by correcting the set temps. of the respective zones with the set temp. correcting signals that take the treating capacity and in-furnace residence time of steel materials into consideration.

CONSTITUTION: Steel ingots which are materials to be rolled are heated to rolling temps. in a continuous heating furnace 10 consisting of a preheating zone 12, a heating zone 14, and a soaking zone 16. In this case, the temp. deviation signal d1 between the set temp. signal b1 and actually measured temp. signal a1 of the zone 16 is multipled by the signal which is obtained by multiplying the processing signals l1, l2, of the steel materials corresponding to the load quantity of the ingots to be heated in the zone 14 and the non-drawing out time signal (f) corresponding to the conveying intervals of the ingots and which take the treating capacity of the ingot and the non-drawing out time into consideration, whereby a set temp. correcting signal h1 is generated. If the set temp. of the zone 14 is corrected in accordance with this signal, it is possible to heat all the ingots to be heated to the target set temps. despite the change in the sizes of the ingot. The zone 14 and the zone 12 are controlled of temps. in the similar manner as well.