PURPOSE: To exercise stable, high-precision control over removal of roll eccentricity, by preventing discontinance of data on the extent of roll eccentricity even when the difference in rotational angle between an upper and a lower backup roll varies during rolling operation.

CONSTITUTION: In a compensating device 12 for the extent of roll eccentricity, upper and lower backup rolls 3a and 3b vary in the difference in rotational angle in accordance with rotational angle signals 6a and 6b of the rolls 3a and 3b to detect the timing where a line (i) in a storage device 7 varies. Then, data are read out of internal storag elements of the device 7 before and after the line (i) varies. When lines (i) and (j) both vary, data are read out before and after the lines (i) and (j) vary. Further, the difference R between the read data is outputted a a compensation signal 14. An adder 15 adds a roll eccentricity extent signal 8 to the signal 14 to output the addition signal 16 for compensating data discontinuance that the signal 8 has during the variation of the line (i) to a roll eccentricity removing device 9, thus, a draft position correction signal 10 is outputted to the device 9.