A controller includes a servo-controller for performing nonlinear and linear control of the read/write position according to an error signal to drive an actuator for driving the pickup; a switch for switching the servo-controller from open-mode to closed-mode according to the error signal; and an adjuster for adjusting the gains of the nonlinear and linear control so that the nonlinear control component is larger than the linear control component at the time of switching and the linear control component is larger than the nonlinear control component after the elapse of a predetermined time from the time of switching.