To manufacture a rolled stock of desired square section by small number of calibers by providing a plurality of flat calibers in an alternately orthogonal to each other in a final finishing process, and alternately repeating the draft of a longitudinal side and a transverse side of an intermediate formed stock with the specified reduction of area using the flat calibers.

A round intermediate formed stock (a) is rolled down in the vertical direction using flat calibers F1 having a horizontal forming surface to obtain an intermediate formed stock (b). The intermediate formed stock (b) is rolled down in the right-to-left direction using flat calibers F2 having a vertical forming surface to obtain an intermediate formed stock (c). The intermediate formed stock (c) is rolled down in the vertical direction using flat calibers F3 having a horizontal forming surface to obtain an intermediate formed stock (d). The intermediate formed stock (d) is rolled down in the right- to-left direction using flat calibers F4 having a vertical forming surface to obtain an intermediate formed stock (e). The intermediate formed stock (d) is rolled down in the vertical direction using flat calibers F5 having a horizontal forming surface to obtain a final rolled product G. When the size is changed, the stroke of the flat calibers F1-F5 is changed.