PURPOSE: To correctly bend without reduced thickness by bending a stock to be formed with both edge faces of the stock compressed in the width direction to obstruct the metal flow to the outside in the width direction of the edge part.

CONSTITUTION: Both edge faces of a stock 9 to be formed face to gate parts 4 formed on an upper roll 7', that is, the roll on the side to be the inner side of the stock 9. Then, by introducing the stock 9 in a roll gap having a development width shorter than that of the strip 9 itself, the contact end faces are subjected to a large compressive stress, and plastic flows are generated in the end parts by the stresses to prevent generation of thickness reduction and underfill. Thus, the structure and adjustment are simplified and the strength and stability are increased.