PURPOSE: To operate rolling and annealing devices smoothly and to maintain good quality of the plate estimating the length of a plate on a looper periodically and each time when there is a factor to change speed, and controlling speed of rolling or annealing to keep the length of the plate within allowable limit.

CONSTITUTION: A looper 20 is provided between a continuous cold rolling device 10 and a continuous annealing device 12 of the plate SP. The plate length pattern 30 is calculated from a rolling speed pattern 26 and an annealing speed pattern 28 extending from present time t=0 to completion of rolling of a present coil and a next coil, and the rolling speed, and the annealing speed etc. are so controlled that the looper 20 does not become below the minimum length L0. In case of work such as rearranging rolls etc. that gives change in rolling speed, the estimated time of completion of the whole process is determined each time when each process is completed. When the time exceeds the estimation, the speed pattern 26 of the rolling device 10 is changed, and the plate length pattern 30 caused by the change is calculated, and the minimum necessary change of annealing speed is performed.