Patent ID: 7397750

Claim:
An optical disk apparatus for reproducing data from an optical disk having synchronization information only once every predetermined information unit, wherein said predetermined information unit is a frame, said synchronization information items being formed such that polarities are arranged alternately as a mark and a space, the apparatus comprising: means for radiating a laser beam on said optical disk; means for receiving a laser beam reflected from said optical disk and outputting said received laser beam as a reproduced signal; means for extracting said synchronization information from said reproduced signal; and means for verifying said extracted synchronization information through use of a rule for alternately arranging said mark and said space; wherein, when said synchronization information detected in said frame is a space, said verification means verifies correctness of said synchronization information extracted in the next frame by means of determining whether or not a synchronization information detected in said next flame is a mark, and if a mark is not detected in said next frame, a synchronization error is determined by said verification means, in accordance with said rule for alternately arranging said mark and said space.