A super-resolution material is formed in only a data pit, in a low temperature state of the super-resolution material,
reflectivity of each of a pit portion and a space portion and an optical
phase difference therebetween are set to be sufficiently small, in a high temperature state, and at least the optical
phase difference between the pit and the space is set to be larger than the aforementioned value in an absolute value. Accordingly, by conducting
irradiation with an appropriate read power by which substantially only one data track width can be heated to a high temperature state, a good push-pull
signal can be obtained even with a track
pitch being less than a
diffraction limit. At the same time, by an optical device having functions such as a switching means with a DPP type, an offset correcting means of the push-pull
signal due to lens shift, a shaping means of the push-pull
signal, a learning means of read power, and the like, there is provided an optical disk device that corresponds to the optical disk medium of the present invention and achieves an increase in capacity.