PURPOSE: To record information with an optimum laser power by utilizing the fact that a proportion of the old information remaining area in a light beam spot is changed by the temperature and detecting the temperature of a magneto-optical disk.

CONSTITUTION: The amplitude level of the output signal of a filter circuit 14 is changed in accordance with the temperature of a magneto-optical disk 1 and has such dependency upon temperature that the amplitude level is reduced in accordance with the rise of the disk temperature. Consequently, the actual temperature of the magneto-optical disk 1 is accurately detected when the amplitude level of the output signal of the filter circuit 14 is measured, and the laser power of the semiconductor laser 5 is controlled to the optimum recording power based on the obtained detected temperature.