A wavefront of a laser light is adjusted using a phase correcting element. The phase correcting element includes an electrode layer, an electrode layer arranged facing the former electrode layer, orientation films arranged on a surface facing the electrode layers, and a liquid crystal layer filled between the orientation films. One of the two electrode layers is formed with an electrode pattern (ring shaped electrode) for providing a spherical aberration correcting effect to the laser light within a constant distance from a center of a beam incident diameter, and a continuous electrode is arranged on an outer side thereof. Occurrence of the aberration by a lens shift is effectively suppressed by omitting electrodes arranged slightly on an inner side of the conventional beam incident diameter.