PURPOSE: To prevent the deterioration in an error rate at the time of reproduction by controlling a laser power so that the regenerative signals have a prescribed amplitude value or above in advance and the digital sum values become a minimum.

CONSTITUTION: The data equivalent to one peripheral of trial write tracks provided on the prescribed place of a disk are recorded, reproduced and amplified by an RF amplifier 2. The outputs of the amplifier 2 are inputted to an RF amplitude deciding circuit 3 and a data slicing circuit 4. The circuit 3 judges the outputs and transmits the result to a controller 7. The regenerative signals are sliced at zero positions by the circuit 4, converted into digital signals and outputted to a decoder 6 and a DSV measuring circuit 5. Input values from the circuit 5 are examined by the controller 7 and if the values are greatly deviated to either positive or negative value, the setting of a laser power control circuit 8 is changed so that the values approach to zero and are again recorded on the trial tracks to be reproduced.