Abstract: A plurality of rolls are supported and freely shiftable on a rotating supporting shaft. The rolls have a V-groove with a circular arc at the bottom of the groove. The plurality of rolls are arranged on a swivel table so that the rotating supporting shaft corresponds to the radial direction of the swivel table. A component of force acting on the roll in the direction of the supporting shaft is alleviated by a shift of each roll in the direction of the supporting shaft. This is accomplished by rotating the swivel table with the bottom of a metal sheet tapered cylinder pushed down against the V-groove. Thus, curling on the lower end of the cylinder is accomplished without generating a bulge in the neighborhood of the lower end of the cylinder and without preforming.