PURPOSE: To prevent the thickness at the rear end of a restrained bar mill caused by the variation of friction coefficient from expanding by grasping the change of a friction coefficient between a shell and a roll in rolling and controlling the peripheral speed of each stand roll.

CONSTITUTION: A roll 2 at each stand is driven by a motor 3 and its peripheral speed is measured by a speed meter 4. Rolling load P and motor current value I at each stand and measured respectively by a rolling load meter 5 and a motor ammeter 6. The load of a restrainer 8 to hold the speed of a bar 7 at a fixed value, the motor current value and speed of a drive motor are measured by the respective measuring instruments. These measured values are inputted into a control computer 9. Speeds between the stands are calculated and these calculated values are instructed by the control computer 9 to a motor 2 at each stand. In this way, the thickness of the product is uniformized and the plate thickness at the rear end of the product can be prevented from expanding.