It is an object of the present invention to provide a laser irradiation apparatus which can form a linear beam spot with a short optical path length, form a linear beam spot being long in a long-side direction, and reduce displacement of a condensing point at opposite ends in a direction of its line. In a laser irradiation apparatus having an optical system for shaping a laser beam emitted from a laser oscillator into a linear beam spot having a long-side direction and a short-side direction, the optical system includes a long-side direction condensing cylindrical lens disposed between a first short-side direction condensing cylindrical lens and a second short-side direction condensing cylindrical lens. Displacement of a position of a homogeneous plane is generated by the long-side direction condensing cylindrical lens so that a distance from the homogeneous plane to the second short-side direction condensing cylindrical lens is constant not depending on a field angle.