Abstract: An apparatus for controlling an AC generator in a vehicle, the AC generator including an exciting coil and driven by an engine to generate an AC output which is rectified and fed to a battery, includes a pilot-lamp switching transistor device constituted by a Darlington-connection of transistors, the pilot-lamp switching transistor device having a base and a collector for turning a pilot lamp on/off, the pilot lamp being fed with a current from the battery through a key switch, a resistor connected between the base and the collector of the pilot-lamp switching transistor, an initial exciting transistor for controlling a current for the initial excitation of the exciting coil by the battery, a voltage detection circuit for detecting a voltage of the battery, and a voltage detection circuit switching transistor for controlling a switching operation of the voltage detection circuit.