A semiconductor film formed over a substrate is irradiated by a first laser beam which is incident on a bottom surface of the substrate at an angle and by a second laser beam which is incident on the bottom surface of the substrate at an angle opposite that of the first laser beam and oscillated by an oscillator differing from that of the first laser beam; whereby, part of the semiconductor film is melted, and a portion of the semiconductor film being melted is moved while the positions of irradiation of the first and the second laser beams and are being scanned approximately along the direction of slant for the first laser beam or the second laser beam.