PURPOSE: To surely set rolls by forming the area in which vertical rolls correspond to flanges of a material to be rolled in a projecting arc shape of a radius having a starting point in the center of the roll and the side area in which horizontal rolls correspond to both end parts of a vertical roll in a recessed arc shape.

CONSTITUTION: While each of a pair of vertical rolls 5, 5 and a pair of horizontal rolls 6, 6 are screwed down under a state free of material to be rolled, and zero point set of rolls is carried out easily without backlash. The vertical and the horizontal rolls are of circular arc contact, consequently, when the vertical rolls 5 incline, or, by whichever surface the material is rolled, the dimension of the flange not only can be kept at a fixed state but the difference between the flange thicknesses can be changed in steps. Further, since the contact part of each roll are by two point contact limited to both end parts, the gap between the rolls can set surely. Consequently, it is possible to manufacture a product excellent in dimension, shape and accuracy.