PURPOSE: To prevent the slip and tension fluctuation of a strip due to a current reference value error when controlling the current of a helper roll drive motor based on the current reference value.

CONSTITUTION: The speed of a helper roll is detected by a speed detector 15 to obtain the speed feedback signal, the difference between this signal and a speed reference value is fed to a speed control circuit 16 with a dead zone to obtain the tension correction output, and a current reference value is corrected with this output. The speed of the help roll in a looper is fed back, the operation state of the helper roll is invariably monitored and controlled, thus the current reference value is corrected to eliminate an error, and a slip and a tension fluctuation are not generated.