To provide a laser beam machining method capable of easily identifying a child substrate occurring error, and enhancing the working efficiency.

In the laser beam machining method for machining a hole in a workpiece 5 by applying the pulse-like laser beam 2 to the workpiece 5, the specifications of the laser beam 2 (the permissible range of the energy intensity, the permissible range of the inclination of the optical axis of the laser beam 2, or the like) are determined in advance, and if the applied laser beam 2 is deviated from the specifications, an identification mark 20 indicating that the workpiece 5 is defective is machined on the workpiece 5 by the laser beam 2. Any defective workpiece 5 can be easily identified by the identification mark 20. Further, any worker need not be intervened therebetween, the working efficiency can be enhanced.