PURPOSE: To assure specified quality for a post stage and to quickly detect the abnormality of a prestage in rough rolling of steel products, more particularly steel ingot by comparing the results of the comparison between the driving power consumption of each pass of rolling mills and the reference value of the time required for rolling with an abnormal pattern.

CONSTITUTION: The rolling mills 2, 1 respectively have, for example, 2, 4 passes. The material of approximately the prescribed temp., size shape and weight is fed to the former. The driving power consumption P, rolling start and end time T and material weight W of a mill motor 3 is converted to a digital value by an analog-to-digital converter 5 and is continuously inputted in real time to a CPU 6. The driving power consumption and rolling time required for rolling per unit weight in each pass are calculated in this stage and the corresponding reference rolling pattern of a disk file 7 is called by a keyboard 8 to the CPU 6 which compares the calculated values with the respective reference values. The CPU identifies whether said pattern corresponds to which abnormal pattern and displays the same on a display device 9 if there is the abnormality in the driving power consumption of the rolling in each pass.