To provide a laser beam machining method having a novel structure in which deviation of an incident laser beam between a desired position and an actual can be reduced when the deviation takes place by thermal expansion of a substrate to be worked.

(a) A substrate to be worked is prepared in which a plurality of incident positions to be machined by irradiation with a laser beam are defined and in which, at least on some incident positions, an alignment mark is formed, wherein a relative positional relation is determined with each incident position. (b) One alignment mark is detected, and on the basis of such detected position, alignment information is obtained for the incident position and the laser optical axis corresponding to the alignment mark. (c) On the basis of this alignment information, laser beam irradiation is performed at the incident position corresponding to the detected alignment mark. (d) Finally, the processes (b) and (c) are repeated at least once for the incident positions unirradiated with the laser beam.