The present invention is to provide a laser irradiation technique for
irradiating the irradiation surface with the laser beam having
homogeneous intensity distribution using a cylindrical lens array without
being affected by the intensity distribution of the original beam. A
laser beam emitted from a laser oscillator is divided by two kinds of
cylindrical lens arrays into a plurality of beams, which are two kinds of
linear laser beams with their energy intensity distribution inverted each
other, and the two kinds of linear laser beams are superposed in a
minor-axis direction. This can form the linear laser beam having
homogeneous intensity distribution on the irradiation surface.