Method of overwriting information on recording material

A method of optically writing an information over an information recorded on a recording material which is reversively convertible between a stable phase and a metastable phase to show different light reflection or transmission by controlling a heating condition to be applied to the recording material wherein the recorded information is recorded in the form of a plurality of separated metastable-phase areas on a stable-phase area is disclosed. One method comprises two steps of erasing the recorded information by intermittently irradiating the plurality of metastable areas,with a laser beam which gives such a high thermal energy to the recording material at least at its central area of a beam spot formed on the recording material as to be able to convert the metastable phase into the stable phase under the condition that the central area of one beam spot is formed on the recording material in an area overlaping with an area of a central high thermal energy area of a laser beam spot having been formed by the preceding irradiation to convert a metastable phase into a stable phase and then recording another information in the recording material by irradiating the recording material with a laser beam to form a plurality of separated metastable-phase areas. Another method comprises a single process for erasing a recorded information, at a desired moment in the course of which a fresh information is recorded by prolonging interval between two laser beam irradiations.