To obtain a phase transition type optical disk by which the shortcoming of the medium, that conducts a mark edge recording and a land/groove recording together, is eliminated, the overwrite characteristic is maintained in a desired mark edge recording and a high density recording is conducted.

The optical phase difference of the reflected laser light beams in the crystalline condition and the noncrystalline condition of a phase transition recording film 3 is set to 180 degrees ±5 degrees. Moreover, the ratio of the absorbing rate of the light beams of the film 3 in a crystalline condition to that in a noncrystalline condition is set to 0.9 to 1.1. Furthermore, the optical depth of the guiding grooves formed on a substrate 1 is set between λ/9 to λ/6 where λ is the wavelength of the laser light beams used. The wavelength of the laser light beams is set within 635 to 650nm and the depth of the grooves is set between 40 to 70nm. In the optical disk, the groove region during a land section reproducing and the land region during a groove section reproducing are optically made equivalent so far as the reflected light beams are concerned.