A system for directly and instantaneously controlling the exciter of a generator. A voltage error calculator calculates a voltage error of output voltage of the generator which is regulated by an instruction voltage and a time constant. A switching signal generator generates switching signals in response to the voltage error. An exciter controller controls the exciter in response to the switching signals. Thus, the system can induce the maximum response characteristic of a power converter only by setting the time constant of a controller without a complicated design for determining gains of the controller. Further, the system can considerably inhibit overshoot from occurring in a transient response state.