When a distortion of an output waveform of an alternating-current generator is improved, an output voltage control apparatus of a generator, which has versatility, is obtained. An output voltage control apparatus of a generator (1), including a generator winding (2) and an excitation winding (3) wound around a stator side, a field winding (5) wound around a rotor (4), and a rectifier (12) for rectifying a current generated by the excitation winding (3) and supplying the rectified current to the field winding (5), the output voltage control apparatus includes a field current drive means (20) for comparing an output voltage generated to the generator winding (2) with a reference wave whose distortion ratio is 0% and flowing a field current to the field winding (5) by adjusting a drive timing of a PWM signal output by a drive unit (24) based on a result of the comparison.