Patent ID: 7224653

Claim:
An optical disk unit that emits light beams from an optical transmission layer, thereby recording information or reproducing information into or from an optical disk having a plurality of recording layers divided in a thickness direction and a light transmission layer protecting a recording layer positioned at the outermost side, said optical disk unit comprising: a light source that emits a light beam used for recording information into an information recording layer targeted for recording and reproducing information from an information recording layer targeted for reproducing; an objective lens that transmits the light beam from said light source through the light transmission layer of the optical disk, thereby focusing light on the information recording layer of the optical disk; a spherical aberration correction mechanism provided between said light source and said objective lens, the mechanism controlling a degree of a spherical aberration caused by the thickness error of the light transmission layer of the optical disk recorded in a predetermined position of the optical disk; a spherical aberration correction mechanism control unit that controls an operation of said spherical aberration correction mechanism based on thickness error information of the light transmission layer of the optical disk recorded in a predetermined position in the optical disk; a light emission intensity control unit that controls intensity of the light beam emitted from said light source based on information of the light transmission layer recorded in the optical disk; and a gain adjustment that provides a predetermined gain based on the distance between the recording layer on which the light beam emitted for recording/reproduction is presently focused by the objective lens and the light transmission layer, for a control value inputted into said light emission intensity control unit.