PURPOSE: To stablish accurate temp. control method in the case of executing continuous heating treatment in a continuous annealing furnace by joining steel sheets having different conditions in dimension, aimed sheet temp., material quality, etc.

CONSTITUTION: At the time of executing the continuous treatment to the preceding material and the following material having different conditions in the continuous annealing furnace, at first, the order of priority to the preceding material and the following material is decided based on the sheet thickness, the preset aimed temp. and torelance in the sheet temp., and a sheet temp. responsive curve from the preceding material to the following material, in which the length of out of the sheet temp. in the material at the priority side becomes zero and length of out of the sheet temp. in the material at non-priority side becomes the min. value and changing timing for setting line velocity for realizing this and the furnace temp., are calculated under presuming and also, based on this, the line velocity and the furnace temp. are controlled, respectively.