In a magneto-optical disk drive using a domain wall moving magneto-optical recording medium, a test-writing operation adjustment to deal wit dynamic fluctuation factors is minimized, and a reproducing or recording laser power is automatically optimized. A power of a light beam by which a domain wall starts to move is detected, and a power of a laser used to reproduce or record an information is corrected based on a change in the domain wall movement starting power. As the domain wall movement starting power, it is possible to use, for example, when the power of a light beam is varied, such a power as to maximize a rate of change of the amplitude of a reproducing signal.