An automatic voltage regulator of a generator with a function for suppressing an overshoot which regulator keeps an output voltage at a predetermined voltage by controlling exciting currents of the generator with turning a switching device on and off, and comprises a voltage detection means for detecting the output voltage of the generator; a deviation calculation means for calculating a deviation for a target with respect to a detected detection voltage; an integral-value calculation means for calculating an integral value of the deviation; and a pulse signal calculation means for calculating the pulse width based on an integral coefficient, a proportional coefficient, the deviation, and its integral value, and for outputting said pulse width as a pulse signal, wherein when before voltage establishment the detection voltage is not less than the first reference voltage, the target voltage is replaced with the set voltage; and wherein the switching device inputs the pulse signal calculated by the pulse signal calculation means.