PURPOSE: To easily perform the dressing of the abrasive grain layer of grinding wheel of an on-line roll grinding device even in narrow space in a rolling machine and to keep roll surface roughness after roll grinding constant.

CONSTITUTION: A dressing grindstone 8 (8a, 8b) consisting of a diamond abrasive grain layer, etc., is loaded on one terminal of a rolling roll 1, and the abrasive grain layer 50 of the grinding wheel 20 is brought into contact with the dressing grindstone 8 by the grindstone sending device of the on-line roll grinding device as rotating the dressing grindstone 8 with the rolling roll 1. The dressing of the abrasive grain layer 50 of the grinding wheel 20 can be performed by rotating the grinding wheel 20 so as to keep surface velocity difference with the dressing grindstone 8 by a grindstone rotating device.