PURPOSE: To provide a method and device for on-line measuring profile of rolling roll with simple structure and small space for mounting to a rolling mill and with which the state of roll surface in rolling rotation can be observed as occasion demmands.

CONSTITUTION: This device is made of such simple structure that a roll shape detector 22 and reference position detector 23 are mounted on the wheel spindle stock 13 of an on-line roll grinder 10, a piano wire 24 as reference is attached to the housing 3 of rolling mill and a moving mechanism for detector is obviated. This device is moved in the axial direction of roll while shape detection is executed at fixed intervals in the circumferential direction by controlling measurement with a controller 27 by the signal from a rotational angle detector 26 which is attached to a roll and the detected roll shape is corrected by the variation of reference position. Roll shapes in the axial direction at the same rotational angle position are arranged and the roll shapes in developed state are displayed with a picture display device 28 and the state of rail surface can be observed as occasion demands.