PURPOSE: To allow overwriting with a single laser beam by changing the power of the laser light to be projected to the medium laminated with magnetic layers varying in the temp. characteristics of coercive force and imparting the bias magnetic field larger than the coercive force in the same direction.

CONSTITUTION: The layer 2 at the lower working temp. of the medium laminated with the 1st, 2nd magnetic layers 1, 2 which vary in the temp. characteristics of the coercive force is formed to have the coercive force larger than the coercive force of the layer 1 and smaller than the optimum bias magnetic field. The magnetization of the layer 1 is zero and the magnetization of the layer 2 is small if the medium is irradiated with the laser light PH for recording; however, the magnetization of the layer 2 is inverted by the temp. characteristics if the bias magnetic field Hex is imparted thereto. The magnetization of the layer 1 is inverted as well by the exchange bonding strength as the medium is further cooled. The recording is thus executed. the magnetizations of the layer 2 and the layer 1 are inverted and the erasing is executed when the medium is irradiated with the laser light PL of the small power for erasing and is imparted with the magnetic field Hex. The overwriting is thereby enabled by changing the single laser beam.