SERVO CIRCUIT

PROBLEM TO BE SOLVED: To realize a servo operation exhibiting high anti-vibration characteristics against not only for external disturbance having a previously known period but also for external disturbance with a varied frequency or external disturbance having an unknown frequency without involving an increase in size due to a large-size anti-vibration mechanism or an increase in cost due to the use of a complicated actuator. SOLUTION: A servo circuit includes an external disturbance frequency detecting section 5 for detecting an frequency of periodic external disturbance included in a servo error signal SE, one or more selective servo signal generating circuits 4 each having a sift register (S, R) with a length corresponding to a period of the periodic external disturbance and extracting period components of the periodic external disturbance from the servo error signal SE, a phase compensation circuit 6 for suppressing any external disturbance components other than the periodic external disturbance included in the servo error signal SE, and an adder 11 for adding outputs of the selective servo signal generating circuits 4 and an output of the phase compensation circuit 6. An output of this adder 11 is used as a servo control signal to an actuator 13.