A vehicle AC generator control device, comprises: an AC generator with a field coil; a rectifier for rectifying an AC output of the AC generator; a battery connected to an output terminal of the rectifier; a voltage regulator with a switching element series-connected to the field coil, the voltage regulator detecting a terminal voltage of the rectifier or battery to operate the switching element to control a field current of the field coil to adjust an output voltage of the AC generator to a predetermined value; a field coil exciting power source for providing an output voltage which is higher than the output voltage of the AC generator; and a field current limiter for limiting a maximum conduction rate of the switching element according to a speed of rotation of the AC generator.