Patent ID: 7817508

Claim:
An optical disk unit for reading signals stored on an optical disk medium, comprising: an optical pickup for selectively irradiating light of one wavelength, from several mutually different wavelengths, to an optical disk medium by means of a single objective lens, and outputting signals based on light reflected by the optical disk medium; a drive section for relatively moving an objective lens of the optical pickup with respect to an optical disk medium surface; a signal output section for receiving light reflected by the optical disk medium and outputting received light signals based on the received light; and a control section for detecting, while the objective lens is being moved relative to the optical disk medium surface by the drive section, a surface reflection of the optical disk surface and, after the detection of the surface reflection, a peak level of a fake signal generated in the received light signal, the fake signal corresponding to stray light occurring inside the optical pickup, comparing the received light signal with a threshold value that is set based on the detected peak level, and detecting reflected light of a data storage layer.