To stabilize processing width and processing depth by making a shape of laser beam radiated to a substrate within a predefined value.

A substrate processing device radiates short-pulse laser light along a processing schedule line on a fragile substrate surface while moving at a predetermined speed, and sprays a cooling medium to a heating position after the laser light is moved. By controlling a pulse interval and a repeating frequency during laser processing, heat generation by laser radiation during processing is controlled, and deformation of a fragile substrate due to diffused heat is prevented. An interval between a processing head and the substrate during movement is controlled to almost identical height by head position adjustment means.