PURPOSE: To relatively easily express intermittent pattern, wavy pattern, etc., in an uneven shape by engraving a specified pattern by the rotary contact of a roller engraving part in the longitudinal direction of the Al surface in a heated softening state.

CONSTITUTION: The Al form 7 subjected to extrusion forming is fed to a pattern device 8 and also led to the small gap between a heat resistant roller 9 and backing guide 11 and the center link piece thereof is passed through compactly. The passing thereof is performed with rotating the heat resistant roller 9 and backing guide 11 in order by the travel of the Al form 7. At this time, the Al form 7 is in a heated softening state and the specified recessed or projecting pattern corresponding to the engraving part 10 of the roller 9 is expressed by engraving it on the Al form 7 surface with the engraving part 10 of the overheated roller 9 being subjected to rotary contact therewith at its passing time through the small gap.