An optical disk can detect reliable address data without the need of checking the validity of synchronous detection of segment numbers. The optical disk has one or more tracks, and address data is arranged in a distributed manner on the tracks. A generating polynomial that generates an error detection code of a segment number included in the address data, which represents location information in the disk rotatory direction, is made different from a generating polynomial that generates an error detection code of a track number included in the address data, which represents location information in the disk radial direction.