In a disk storage apparatus having an actuator for loading/unloading a magnetic head with respect to a magnetic disk, a voltage signal generated when the actuator is driven is detected by a voltage detector, a speed load estimator estimates moving speed of the head and level of load disturbance added to the magnetic head from a driving signal in a driver of the actuator and the voltage signal, and outputs a speed estimating signal and a load estimating signal, a speed controller generates and outputs a speed control signal based on a speed command signal and the speed estimating signal, a synthesizer generates a driving signal from the load estimating signal and a speed control signal, and the apparatus loads and unloads the head at a stable speed against the load disturbance caused by friction or the like on a ramp block.