PURPOSE: To enable high quality machining with no residue of removed matter by projecting laser beams on a glass substrate having a formed thin film from the substrate side and by vacuum-sucking the substrate from the thin film side.

CONSTITUTION: A thin film 2 for a metal electrode or the like is formed on a substrate 10. Laser beams 60 are projected on the substrate 10 from a position above the substrate 10 and focused on the film 2. The film 2 absorbs the energy of the beams 60 and the projected part of the film 2 is converted into plasma and separated from the substrate 10. At the time. the substrate 10 is vacuum- sucked from the film 2 side. Since a groove 53 for vacuum suction has been cut under a groove as the machined part of the film 2, the separated part drops in the direction of arrows 61 by the synergistic effect of its own weight, a plasma jet and the vacuum suction. Thus, the thin film 2 is machined in a high yield.