PURPOSE: To reduce the oscillation phenomenon of the control system by piling the analog signals of the A/D converter to those of the D/A converter and then controlling the controlled unit with these piled signals.

CONSTITUTION: The analog signal output of controlled unit 1 which is controlled by the control analog signals, and the controlling analog signals are generated from the detected signals. These analog signals are converted to the digital signals via A/D converter 2, and the digital process necessary for control of unit 1 is given through digital processor 3 to carry out the conversion into the digital signals through D/A converter 4. The output of the digital signal is supplied to analog piling circuit 5 to be piled on with part of the analog signals sent from circuit 1. These piled analog signals are supplied to unit 1 for the automatic control of unit 1. Thus, the delay of the response velocity of converter 4 is corrected by piling of the analog signals thus to prevent the oscillation at the control loop. In this case, the analog signal must be smaller than the signal obtained through converter 4.