PURPOSE: To eliminate a high band component and to reduce the noise generated from an actuator, by eliminating the PCM signal leaked into a tracking error signal without changing the characteristic of a tracking servo loop.

CONSTITUTION: A delaying device 9 is connected to the output of a detector 4-1 to delay the output of the detector by a time equivalent to the delay time τ between light spots 1 and 2. Both spot 2 and an optical detector 4-2 have the same PCM signal while the outputs of the preceding spot 1 and the optical detector 4-1 are delayed by the time τ. Therefore the PCM signal component is equal among input signals of a differential amplifier 6, and the output of the amplifier 6 contains no PCM signal component. As a result, no PCM signal component is contained in the input signal of a tracking servo actuator 8. Thus no noise is generated from the actuator 8.