Patent ID: 8451698

Claim:
An optical disk reproducing device comprising: a signal reproducing section configured to read and decode information recorded on an optical disk by an optical pickup unit, and reproduce the information, wherein said signal reproducing section includes a gain controlled amplifier circuit configured to amplify an radio frequency signal generated from a light receiving element, an automatic gain control circuit configured to control a gain of said gain controlled amplifier circuit, and a signal processing section configured to derive a part of an automatic gain control value generated in said automatic gain control circuit, and generate a control signal for adjusting one of an optical system path and a detection system path for controlling said optical pickup unit, wherein said signal processing section includes a digital arithmetic processing section configured to obtain a focus bias value from a characteristic curve relating a focus bias of the optical pickup unit and a controlling gain value corresponding to the automatic gain control value, the focus bias value being obtained by varying said focus bias to determine where the controlling gain value on the characteristic curve assumes an extremum and determining the focus bias value corresponding to the extremum, wherein the signal processing section adjusts said optical pickup unit by further optimizing the focus bias value in correspondence with a perturbation value α.