US Patent 7796478 Optical disk apparatus

The whole reflection signal and a tracking error signal are detected while an objective lens is being moved in the radial direction of an optical disk, and the temporal difference between a time at which the value of the whole reflection signal becomes a maximum and a time at which the value of the tracking error signal becomes zero is detected in a predetermined time period. In addition, a value which is obtained by dividing the temporal difference by the time period of one cycle of the tracking error signal is acquired as a tilt appearance magnitude. Relational information in which a tilt appearance magnitude and a tilt correction magnitude corresponding to the tilt appearance magnitude are associated is read out, and the relational information read out and the current tilt appearance magnitude detected by a tilt-appearance-magnitude detection circuit are compared, thereby to determine the tilt correction magnitude necessary for a tilt correction. The tilt correction magnitude is notified to a tilt correction circuit, and is used in making the tilt correction.