An optical disk is made up of a disk-shaped substrate having a surface, a first track and a second track provided on the surface of the substrate, where the first and second tracks are two mutually adjacent concentric tracks or two mutually adjacent track turns of a single spiral track, the first track extends along a first center line and the second track extends along a second center line, and an identification signal recording part extending along a third center line and prerecorded with an identification signal including at least a sector number and a track number for identifying a position on the optical disk. The third center line is arranged between the first and second center lines, and the identification signal prerecorded in the identification signal recording part is common to the first and second tracks on both sides of the identification signal recording part.