PURPOSE: To comparatively quickly produce an indicia on a diamond without requiring an expensive computer-driven X-Y table by producing the indicia on the diamond with a pulse excimer laser.

CONSTITUTION: This method is composed of a process for arranging a mask 23 between the output port of an excimer laser 11 and a surface part 17 of a diamond 15 to be marked (a) and a process for directly irradiating the surface part 17 of the diamond 15 with the excimer laser 11 through the mask 23 so as to form the pattern of the mask 23 as a mark with the irradiation of the excimer laser 11 (b) (24 is optical reduction means). This excimer laser irradiates the diamond with the waveform of about 193 nm and at least one pulse.