A drilling method and a laser machining apparatus which can shorten the measuring time of workpiece surface height and improve the machining efficiency in spite of irregularities of about 10-30 μm high in the surface of a table. Surface heights of the table is measured at lattice points in advance. Top surface height at a desired point of the workpiece mounted on the table is measured. Surface height of the point is arithmetically obtained using heights of four points surrounding the point. The difference between the measured height and the arithmetically obtained height is set as the plate thickness of the workpiece. Top surface height of the workpiece at a machining position is regarded as the sum of the plate thickness and the height at that position obtained from the table surface heights.