in a reversible memory system, a pulsed laser beam generated from a laser unit is directed to a recording layer (2) formed on a substrate 1. The recording layer (2) essentially consists of a recording medium, for example, an iron-nickel alloy containing iron as a mayor component and 27 to 30 atomic % of nickel, which undergoes martensite transformation from a low-temperature phase (D) to a high-temperature phase (E) at a predetermined temperature Af and which undergoes a stress-induced transformation (a 2 ) at a characteristic temperature Md. When a region of the recording layer is irradiated with the laser beam having a predetermined intensity, the region undergoes a stress-induced transformation (a 2 ) so that the region is changed from the high temperature phase (A) to the low temperature phase (8).