PURPOSE: To prevent the occurrence of a slip by changing driving torque ratio by tension of a strip before and behind a bridle roll to equalize each coefficient of friction between the strip material and the bridle rolls in a steel process line.

CONSTITUTION: Tension Fe and Fd of a strip St before and behind a bridle roll BR are compared with each preset value of rheostats RH1, RH2 to drive motors M1, M2 through respective current control devices ACR, converters of thyristors. Both tension signals Fe, Fd are processed by CPU to find current ratio set values Ke, Kd for motors Me, Md on input side, thereby driving both motors through a control circuit CON to change the driving torque ratio therebetween, so as to equalize each coefficient of friction between bridle rolls Re, Rd and the strip material St. Thus, the possibility of a slip between the bridle rolls and the strip can be lessened to improve the reliability of drive.