1. A control apparatus for controlling a servo-mechanism, the servo-mechanism including a control object, the control object having an input for receiving a first operation signal and an output for outputting a control signal in response to the first operation signal, the control apparatus comprising: a first control signal loop including the control object, detecting means for detecting the control signal from the control object and generating an actual control signal representing the detected control signal, and means, responsive to the actual control signal and a desired control signal representing a control signal desired to be output from the control object, for generating a second operation signal for causing the actual control signal to become equal to the desired control signal; and a second control signal loop including the control object, the detecting means, means, responsive to the actual control signal and the first operation signal, for generating a model-based operation signal, and means, responsive to the second operation signal and the model-based operation signal, for generating the first operation signal such that the first operation signal causes the second operation signal to become equal to the model-based operation signal.