A rectangular beam having the energy density distribution homogenized in its short-side direction is formed in a beam homogenizer wherein two light reflection surfaces are parallel-provided in a beam progression optical waveguide with a predetermined space so as to face each other at surfaces along the beam progression direction and a course change reflection surface for changing the beam progression direction is formed at a surface in the direction intersected with the light reflection surfaces. The beam enters a cylindrical lens array and a cylindrical lens sequentially to homogenize the energy density distribution in its long-side direction. Then, the irradiation laser from the cylindrical lens is projected onto a non-single crystalline semiconductor film to perform annealing.