PURPOSE: To reduce the roll exchanging time by providing a spline on the end part on the drive side of a roll shaft to be fitted in a spline hole, and providing a screw on the end surface on the work side of the roll shaft for the release-stop to make possible the exchange of the roll shaft together with a work side stand.

CONSTITUTION: A roll shaft 31 is withdrawn from a drive side stand by removing fixing bolts of a work side stand and sliding the stand in the direction of the roll shaft. The integrated set of the roll shaft 31, a roll 32, the stands, etc., is lifted by a crane to be moved. Another set which is prepared out of the line is lifted by the crane, and slid on a bed in the direction of the roll shaft, and a spline 31c of a driving part of the roll shaft 31 is fitted in a spline hole of a drive shaft 16. Then, a work side stand is fixed to the bed by bolts. For the removed stand, a roll shaft 31 is withdrawn from the work side stand and a roll shaft fixed with the roll 32 of different size is again inserted to the stand and fixed thereto.