PURPOSE: To properly adjust the driving of a turning-back roll by analogizing dynamically a friction drag occurring between a steel and liquid and between a turning-back roll and the liquid, etc., and attaining a current compensating value according to the states of the steel, the liquid, the turn-back roll, etc.
CONSTITUTION: The flow rate of liquid 3a in the vicinity of a steel 2 is detected by a flow rate detector 9, and a friction drag between the steel 2 and the liquid 3a is analogized by a friction drag arithmetic unit 10. And, a current compensating value is outputted from a submerged resistance compensator 8 according to this analogized friction drag. Thus, the driving of a change-direction roll 4 is adjusted through a motor 5. Therefore, even when the flow rate is changed by the surface condition of the steel 2, the viscosity of the liquid 3a, etc., the tension of the steel 2 is controlled in a desired state.