To provide a method of a laser beam machining, by which plural holes are drilled at a pitch smaller than the wave length of the laser beam.

Plural holes to be drilled on a material are divided into two groups. The pitch of the holes of the first group is set beyond a hardening zone accompanying the laser beam machining. The pitch of those of the second group is set in a region which does not deviate from the hardened zone around the holes of the first group. The holes of the first group are drilled by using a laser beam which is set at a specified energy level or pulse numbers, then the energy intensity of the laser beam is enhanced up to an energy level higher than the threshold value of the ablation of the hardened material, and the holes of the second group are drilled.