PURPOSE: To provide multi-valued recording and to attain a high recording density without changing a recording mark and a beam diameter of irradiation light, etc., in the optical recording and reproducing method utilizing a change in intensity of reflected light on an optical recording medium.

CONSTITUTION: Recording is performed by forming a diffraction pattern for obtaining diffracted rays 20 having different diffraction angles θ in accordance with recording information in a unit recording mark part 14 of the optical recording medium 1, and reproducing is performed by detecting the plural diffracted rays 20 to be emitted as an information signal by irradiating this unit recording mark part 14 with the light beam 18. This diffraction pattern is formed by utilizing an entangled pattern by spinodal decomposition of a phase separation type recording material in addition to a diffraction grating.