When a method for increasing density by providing a tracking guide such as a land/groove and introducing a plurality of strings of super-resolution pits into one track thereof is applied to a reproduction-dedicated optical disk, there are problems in that the production cost is increased, the structure is complicated, and the space which can be used for a recording pits is narrowed because of the land/groove structure.In the invention, a concept of group tracking is applied. One track is formed by a plurality of pit strings having a size not greater than the optical resolution limit in the radial direction and a size not less than or not greater than the optical resolution limit or only not greater than the optical resolution limit in the tangential direction. Reproduction of the super-resolution pit itself is performed by using a non-linear phenomenon generated locally, but, in tracking, a plurality of strings of pits are considered to be one track, and detection of the movement of a laser light for read out is realized by the method used for an existing optical disk by using a reflected light or a transmitted light from the optical disk.