Patent ID: 8107347

Claim:
An optical disk apparatus, comprising: a light source that emits a light beam; an objective lens that condenses the light beam to a target recording layer to be a target of one or two or more recording layers provided on an optical disk; a condenser lens that condenses a reflected light beam after the light beam being reflected by the optical disk; a hologram device that, when the reflected light beam is caused to travel in a straight line or diffract to separate into a reflected zero-order light beam and a reflected primary light beam, causes a portion of the reflected primary light beam to diffract in a predetermined first direction by a first region to create a first beam and causes a portion of the reflected primary light beam to diffract in the first direction by a second region to create a second beam; a photo-detector that generates a received light signal by receiving the first beam and the second beam by a first receiving region and a second receiving region, respectively, provided at an irradiation position of the reflected zero-order light beam on a side of the first direction; and a signal processing unit that generates a preformatted signal representing preformatted information recorded in track grooves of the optical disk in advance based on the received light signal generated by each of the first receiving region and the second receiving region, wherein the photo-detector includes a zero-order light receiving unit provided at the irradiation position of the reflected zero-order light beam and divided into a plurality of receiving regions, and wherein the signal processing unit includes a switching circuit capable of selecting one of the received light signal generated by each of the plurality of receiving regions of the zero-order light receiving unit and the received light signal generated by each of the first receiving region and the second receiving region as the received light signal used for generating the preformatted signal; and, if the switching circuit selects the received light signal generated by each of the plurality of receiving regions of the zero-order light receiving unit, can generate the preformatted signal based on the received light signal.