A track search controller has three two-segment photodetectors, three subtracters associated respectively with the two-segment photodetectors, a processing circuit, and a servo control cirucit. Each of the photodetectors produces two output signals based on a light beam reflected from an optical disk. Each of the subtracters produces a differential output signal representing the difference between the output signals from the associated photodetector. The processing circuit generates an actuator position signal from the output signals from the subtracters. The actuator position signal contains a component indicative of a deviation of the actuator due to its vibration. The servo control circuit controls an actuator, which actuates a laser beam source, so that the actuator position signal will be of a constant value.