PURPOSE: To prevent misrolling and to improve operability by keeping the mass- flow at a looper on the downstream side constant, by changing the rolling speed between stands placed on the upstream side basing on the change of mass-flow at the looper placed on the downstream side.

CONSTITUTION: The front end of a material enters the (i+1)th stand, and thereafter a loop is formed. This timing is detected by a detector 2, and an output of a height controlling device 3 at this time is stored by a device 4 for outputting a deviation of loop. And thereafter, the stored value is constantly compared with an output of the device 3 by the device 4 to output its deviation to a device 5 for outputting a deviation of tension. In the device 5, the deviation of loop is calculated as the deviation of tension, and the result is inputted to a device 6 for controlling a tension between stands. Then as against a set value T of initial tension, a deviation ΔT of tension is added to the set value to obtain a target value of tension T+ΔT, thereby the target value is used for controlling.