PURPOSE: To prevent a material to be rolled from the generation of flaw and an electric power converter from tripping, by detecting the sheet thicknesses at the inlet and outlet sides of the material, and changing the carrying speed of a table of the material basing on a specific relative equation, at the time of changing the sheet thickness of the material during running.

CONSTITUTION: When the sheet thickness of a material to be rolled is changed steeply while the material is rolled by a mill, the sheet thickness h1 at the inlet side of the material of the mill and the sheet thickness hO at the outlet side are detected. Next, the carrying speed VTi of a table of the material is obtained from said thicknesses h1, hO and the roll speed VR of the mill basing on the equation. Thus, a slip, etc. of the material on the table is prevented by conforming the carrying speed of the table to the speed of the material.