PURPOSE: To easily execute the intrasurface bending by setting the interval clearance of the conical rolls so as to be little at the large diameter part and to be large at the small diameter part respectively in accordance with its tapered angle and rolling down the rolled stock largely at one end side and small at the other end part and bending it in the plane.

CONSTITUTION: A pair of conical rolls 2, 3 are arranged with its rotary axis inclined to the pass-line of the rolled stock, its inclined direction is small for each conical roll and the center of the end part of small diameter side approaches the pass line of the rolled stock. In this state, the interval clearance of each conical rolls are set so as to be large at the small diameter side and little at the large diameter side. The difference of the outer dimension of the small diameter part and of the large diameter part becomes large, because the each conical rolls are arranged inclinedly and the tapered angle can be taken large. The roll circumferential speed of the small diameter part where the clearance between the rolls is large and the draft is small is low and the roll circumferential speed of the large diameter part where the clearance is small and the draft is large becomes high. Therefore, difference of the feeding speed of the rolled stock and the roll circumferential speed is negligible, the generation of wrinkles and cracks, etc., can be prevented.