Abstract: A control device for an AC generator having an armature coil and a field coil includes a rectifier for rectifying an AC output of the AC generator, which is driven by an engine, to excite the field coil. A storage battery is adapted to be charged by the rectified output of the AC generator rectified by the rectifier for supplying power to the field coil when the engine is started. A switching element switches over a connecting condition of the storage battery in such a manner that the storage battery is connected through the rectifier to the field coil to supply power to the field coil when the engine is started, the switching element being connected to an AC output of the AC generator for supplying the AC output voltage of the AC generator as a drive voltage to the second switching element.