PURPOSE: To stabilize the control of strip temp. in a heating furnace and to improve the control accuracy by controlling manipulated variables such as fuel flow rate based the estimated value without depending the measured value in the strip temp. at an outlet on to a prescribed section at the front part and the rear part of the connecting part of the different kinds of the strip-like material.

CONSTITUTION: In the heatiang furnace 21 for heat-treating the steel strip, the strip temp. at the outlet is measured with radiation temp. through a strip temp. meter 22. Based on the information of the actual values including the measured value and the aimed strip temp., material of the steel strip, strip passing speed, etc., by controlling the fuel flow rate and the other operating quantity setting to the heating furnace 21 in an optimum strip temp. control part 23, the furnace temp. is adjusted. In the strip temp. control method in the heating furnace, in the case of connecting the different kinds of the steel strip drawn out from pay-off reels 26a, 26b in an automatic welding mechanism 24 and continuously passing into the heatiang furnace 21, the position of the connecting part is detected by the steel strip connecting part positioning observation part 25. At the time of executing heat treatment in the vicinity of the connecting part calculated from the strip passing speed, the measured value of the strip temp. at the outlet is made to be invalid and the estimated value is used instead of the above value, or the manipulated variables are fixed at the front and the rear parts.