To provide a method and a device for laser beam machining for making a hole on a work with a laser beam, by which method and device the power of the laser beam source is smaller than that of a case where the laser beam machining is performed by making a work irradiated with the laser beam, whose diameter corresponds to the planned diameter of a hole to be made on the work, and by focusing the laser beam on the work, and the machining time is shorter than that of a case where the laser beam machining is performed by making the work irradiated with a laser beam, whose diameter is smaller than that of the hole to be made, by being scanned along the periphery of the circle of the hole to be made.

The laser beam emitted from a YAG laser oscillator passes through an aperture 111, as shown by a chain double-dashed line in the figure, its optical path is bent by 90 degree at a vertical reflecting mirror 112, then the laser beam enters into a conical mirror 113, and is emitted in a form of a ring laser beam. Further, the ring-formed laser beam emitted from the conical lens 113 is converged by an fθ lens 114, and irradiated as a ring-formed laser beam L having a predetermined width S vertically downward with respect to a work W.