PURPOSE: To mark specified scales on the metallic ruler by controlling the movement of a laser beam oscillator and carrying out image formation and printing of a laser beam.

CONSTITUTION: Printing and marking can be carried out blackly on a scale part 1' of the surface of the square 1 made of stainless steel, for instance by regulating the voltage of a laser beam power source 9 and the irradiation distance, the irradiation time, etc., of the laser beam oscillator 2 to regulate irradiation strength of the laser beam. The scales 3 can be added without carrying out masking, etching, black plating, etc., at all as in the past. Further, when the scales cannot be marked in black according to material, black plating, etc., can be carried out in the conventional way on recessed parts marked by the laser beam. In addition, this invention is a method which can be applied not only to the metallic square 1 but also to a plastic straight ruler body.