PURPOSE: To prevent the generation of the partial elongation and wrinkle of a metallic bar stock by arranging tension cutting devices before and behind a flame processing device.

CONSTITUTION: An aluminum bar stock C which is taken up into a roll shape is fed to a bridle roll 5 above which a burner A is provided through a tension roll 2 and tension cutting devices 3, 4 and flame processing is applied. The rear of the stock is processed with a bridle roll 6 and burner B. The processed bar stock is taken up with a take-up roll 15 through tension cutting devices 8, 9, a tension roll 10, etc. In such a manner, at least one flame processing device 5, A (6, B) is provided and at least one of tension cutting devices 3, 4, 8, 9 is arranged before and behind that. In this way, the flame processing is excellently performed in uniformity of surface properties in the width and length directions and productivity.