PURPOSE: To maintain the thickness of rolled materials with high accuracy with a rolling mill equipped with a X-ray thickness meter, by inputting roll rolling reduction position, rolling down force, and signals of a pulse oscillator and the X-ray thickness meter into an arithmetic control device and controlling a roll rolling reduction driving device with a roll rolling reduction position reference signal obtained from the arithmetic control device.

CONSTITUTION: When a steel plate 9 is rolled with a rolling mill 3, each detected value of a load cell 4 for detecting rolling pressure, a roll rolling reduction location detector 5, a pulse oscillator 6 for measuring the number of revolutions of roll, and an X-ray thickness meter 8 installed to the outlet side of the rolling mill 3 is inputted into an arithmetic control device 10. A reference signal for roll rolling reduction position is outputted from the control device 10 to a roll rolling reduction driving device 7 and the roll rolling reduction position is corrected. When this method is applied, length of off-thickness part at the leading edge of rolled materials is sharply reduced as compared with conventional X-ray monitor controlling method and dimensional accuracy of rolled sheets is improved.