A servo control apparatus for controlling according to a position command signal an object in a mechanical drive system having a position detector.A state observer is receptive of a drive torque signal and a position detection signal from the position detector for processing these signals to estimate concurrently a disturbance torque and velocity of the object to output an estimated disturbance torque signal and an estimated velocity signal.A position control processor is receptive of the position command signal, the position detection signal, the estimated disturbance signal and the estimated velocity signal for processing these signals to carry out positive feedback of the estimated disturbance torque signal and velocity feedback compensation by the estimated velocity signal to thereby produce the drive torque signal effective to control the object and to cancel out an actual disturbance torque generated in the object.