US Patent 7242643 Optical disk apparatus

In an optical disk apparatus, after chucking an optical disk, the optical disk apparatus defers the start of the rotation of the optical disk, and measures the focusing drive voltage at two points, i.e., a point near a center of the optical disk and a point near an outer edge of the optical disk. Then, based on the measured values, the optical disk apparatus determine the angle at which the optical disk is slanted. Therefore, when the optical disk has been chucked inappropriately, the chucking state can be determined without rotating the optical disk, and scratching of the optical disk and damage to the optical disk apparatus can be prevented.