PURPOSE: To execute the stable access action even when a large adjustable speed is used by providing two speed detecting means and setting respective speed detecting gains and the cutting frequencies of LPF as prescribed.

CONSTITUTION: The speed detecting gain of a second speed detecting means 7 is enlarged for a first speed detecting means 6. Cut off frequencies f1 and f2 of the LPF used for respective speed detecting means 6 and 7 are set to f1>f2. Then, even when the access action is completed and the speed of a light beam becomes small, the speed servo system with the small influence of a ripple due to the speed and frequency conversion can be realized and the stable access action can be obtained.