Patent ID: 7764586

Claim:
An aberration correcting apparatus for correcting aberration of a light beam for information recording or reading with respect to an optical disc, comprising: an optical element which is disposed to cross an optical axis of the light beam irradiated onto the optical disc and which can partially change an optical path length of the light beam; a disc judging device for judging a type of the optical disc; a rank setting device for setting a rank corresponding to the type of the optical disc judged by said disc judging device, for each of spherical aberration, coma aberration, and astigmatism aberration; and an optical-element controlling device for controlling a partial change in the optical path length of the light beam on said optical element to remove or reduce the spherical aberration, the coma aberration, and the astigmatism aberration in order in accordance with the rank set by said rank setting device.