PURPOSE: To prevent cracks from generating in forming a cross-sectionally channel shaped article that is bent horizontally.

CONSTITUTION: A long planar blank W which is restrainedly pressed by a die 3 and a puncla 10 is formed into a channel shape in the cross section, and released on the main body 1 of a lower die of the die 3. A slide cam 29 for bending consisting of plural slide cam base pieces 30 is advanced by a drive cam 7, performing horizontal bending on the cross-sectionally channel shaped blank W. In this case, plural slide punches 14 which are part of the punch 10 are slidingly displaced in the horizontal direction, following the contour of the formed article P.