Abstract: A servo control system for controlling position of a readout head such as a magnetic or optical head which records, reproduces or erases information on or from a magnetic or magneto-optical disk. This servo control system includes an actuator for moving the head toward a required position on the disk, a position detecting circuit for detecting a position of the head relative to the disk, and a signal processing circuit for processing an output signal from the position detecting circuit to provide a control signal to the actuator. When a value of the signal from the position detecting circuit falls within a preselected range, a controller deactivates a servo control operation of the signal processing circuit and modifies controlled parameters used in the servo control operation in response to a disturbance such as vibration of the system.