The energy distribution in the short-side direction of a rectangular laser beam applied to an amorphous semiconductor film (amorphous silicon film) is uniformized. It is possible to the energy distribution in the short-side direction of the rectangular laser beam by the use of a cylindrical lens array 26 or a light guide 36 and concentrating optical systems 28 and 44 or by the use of an optical system including a diffracting optical element. Accordingly, since the effective energy range of a laser beam applied to the amorphous semiconductor film is widened and the transport speed of a substrate 3 can be enhanced as much, it is possible to improve the processing ability of the laser annealing.