PURPOSE: To control the breadth of a material to be rolled to a prescribed value, by controlling the circumferential speed ratio of the rolling rolls.

CONSTITUTION: A controlling computer 1 computes the run-out side breadth deviation from information on the feed-in side breadth profile obtained by a breadth gauge 6, etc., installed on the feed-in side of a rolling mill, in consideration of the rolling condition, and then, computes the circumferential speed ratio the most suitable for absorbing the said breadth deviation from a stored model. The result of this computation is inputted to a speed controller 2 as a control reference; then, the breadth is controlled through a controlling action for the circumferential speed difference. The result of the breadth control is measured by a breadth gauge 7 installed on the run-out side of the rolling mill and is fed back to the controlling computer 1; hereby, the model stored in the computer 1 is suitably corrected correspondingly to temperatures, material quality, etc., of the material to be rolled.