PURPOSE: To enable a belt-like metallic sheet to be bent with high precision.

CONSTITUTION: A male die 4 is structured by providing an engaging flanges 3, at spaces apart slightly wider than a belt-like metallic sheet 2, on the surface side at both ends of the male die body 1 that is provided with a surface circular- arcuate in the front part; the belt-like metallic sheet 2 is fitted in a groove formed by each engaging flange 3 in the male die 4 and the male die body 1; then, the male die 4 and a female die 5 arranged in parallel with it are moved so as to be relatively close to each other; and finally, bending is performed on the belt-like sheet material 2.