To reduce the deflection of a roll shaft caused by load during rolling, to suppress variation in thickness in the longitudinal direction of products, to eliminate scrapping of defective products in thickness, deterioration of yield and labor due to cutting-off work and also to improve the quality by putting a belt over roll shafts.

The roll shafts 7 are incorporated in a roll stand 1 through housing 9, vertically deflected by load during rolling and, on the other hand, the load at the time of idle rolling is reduced and, as compared to during rolling, the deflection of the roll shaft 7 is decreased. Then, the clearance between a mandrel and a die 8 is narrowed and the thickness of the products is thinned. To dissolve the those problems, by putting belts 10 over the upper and lower roll shafts and holding the roll shafts 7 in the position nearer to the die 8, the deflection of the roll shafts 7 is reduced and the variation in the thickness of the products is reduced.