A generator control apparatus, for controlling electrical generation operation of a vehicle alternator, has a LAN circuit and a dedicated communication circuit, respectively communicating with an external control apparatus (e.g., engine ECU) via a LAN and via a dedicated signal line. When a selection signal is transmitted from the external control apparatus, designating a specific signal to be transmitted to or from the generator control apparatus, communication of that signal is performed via the dedicated signal line, enabling TDM communication of plural signals via the LAN concurrent with direct communication of a specific signal via the dedicated signal line.