PURPOSE: To seize a roll profile at a temperature in rolling by measuring the distance between the roll surface and a reference line, parallel to the roll axis of a rolling roll, at least at three points i.e. the central part and both ends of roll.

CONSTITUTION: Sensors S1, S2, S3 are arranged on a reference line (bed frame 2) parallel to the roll axis of a rolling roll 1 incorporated in a rolling mill. The positions of sensors S1, S2, S3 are located at three points i.e. both ends and a central part in the axial direction of roll 1. The distances (l1), (l2), (l3) from the frame 2 to the surface of roll 1 are measured. Thus, the amounts of crown throughout the whole length in the roll-axis direction are obtained.