Abstract: An eccentricity compensator for an optical disk player includes an amplifier for amplifying detected phase difference signals and outputting the amplified phase difference signal to a driving circuit, a system controller for recognizing whether a currently played disk surface is the top or bottom thereof and then comparing the error of the velocity controlling amount of a spindle motor with a reference tolerance, so as to output a control signal according to the comparison result, and a gain controller for, in the case of top-surface playback in which the velocity controlling amount is greater than the reference tolerance, controlling the gain of the amplifier in response to the control signal of the system controller, so as to vary the velocity of the spindle motor, and so as to reproduce normally a double-sided disk whose top and bottom surfaces have different eccentricities.