For reproducing and/or recording information from/onto an optical disc, a pickup is used to detect a target track on the disc through an optical beam. In carriage servo control, movement of the pickup is servo-controlled in the radial direction of the optical disc. In this control, a tracking error signal is produced by a preamplifier. A pulse signal is produced, in which the period of the pulse signal is set to a constant amount corresponding to the accuracy of movement of the pickup. Based on the pulse signal and the tracking error signal, a carriage control signal to move the pickup is produced. The carriage control signal is then supplied to a carriage motor by a driver, so that the pickup is moved.