Patent ID: 8238222

Claim:
An optical disk device capable of reproducing an optical disk having three or more recording layers, comprising: a laser diode for emitting a laser beam; a photodiode for receiving light of the laser beam reflected from the optical disk, and outputting a signal based on the received reflected light upon performing photoelectric conversion thereto; an optical system including an objective lens and which collects the laser beam emitted from the laser diode on the recording layer of the optical disk via the objective lens, and guides the reflected light from the optical disk to the photodiode via the objective lens; a signal processing unit for creating a focus error signal based on an output of the photodiode; a processor for detecting the recording layer based on the focus error signal created with the signal processing unit; and an actuator for moving the objective lens of the optical system in a thickness direction of the optical disk, wherein the processor: moves the objective lens in the thickness direction of the optical disk by controlling the actuator, and measures a time interval in which each of the recording layers was detected while moving the objective lens, compares a first time interval from the first detection of recording layer to the second detection of recording layer, and a second time interval from second detection of the recording layer to the third detection of recording layer, determines a focal position of the objective lens based on a comparative result, determines that a surface of the optical disk was erroneously detected as the recording layer if the first time interval is greater than the second time interval by a predetermined multiple that is greater than 1, determines the focal position of the current focal position of the objective lens based on the determination result and the number of recording layers, and moves the focal position of the objective lens on the recording layer that was detected third in the optical disk, and thereafter moves the focal position of the objective lens to the intended recording layer.