The paper describes the control system of the Ispra-1 reactor which has been designed and built by the Servomechanism and Reactor Control Laboratory of the CNEN. The system adopted follows the two channel philosophy, in order to keep to a minimum the stresses of the regulating rod, even when the reactor is very noisy and when high precision in the regulating of the power level is required. The stability of the regulating system during constant power operation and during the constant period transient is analyzed. Results of testing of the real system on a nuclear reactor simulator are reported.