A method for rapidly performing laser irradiation in a desired position as laser irradiation patterns are switched is proposed. A laser beam emitted from a laser oscillator is entered into a deflector, and a laser beam which has passed through the deflector is entered into a diffractive optical element to be diverged into a plurality of laser beams. Then, a photoresist formed over an insulating film is irradiated with the laser beam which is made to diverge into the plurality of laser beams, and the photoresist irradiated with the laser beam is developed so as to selectively etch the insulating film.