PURPOSE: To measure inline the shape of a work roll by moving back and forth a stand having the length extending to the longitudinal direction of the work roll in a way as to be able to enter freely the inside of the space between the work rolls and measuring the straightness of the measuring position of a distance sensor.

CONSTITUTION: A stand 4 and an inserting device 5 are moved by the command of a microcomputer 13 via a stand/inserting device 14 to a prescribed measuring position and are retreated to a non-measuring position. The output from a distance sensor 2 is inputted via a sensor amplifier 15 to the microcomputer 13 which calculates the shape of the work roll. The result of measuring the straightness of the stand 4 or the sensor 2 by a laser straightness meter 12 is inputted to the microcomputer 13 and the measured shape of the work roll is corrected in accordance with the result thereof.