An electric generation control apparatus for a vehicle alternator receives an electric generation control signal transferred from an ECU placed apart from the control apparatus through a data transfer line. The control apparatus has a voltage comparator, a communication state judgment circuit, a serial data communication receiver, a PWM communication receiver, and an electric generation control circuit. The voltage comparator acts as a receiver of receiving the electric generation control signal transferred through the data transfer line. The communication state judgment circuit judges whether the received signal is a PWM signal or a serial data signal. The serial data communication receiver and the PWM communication receiver demodulate an electric generation control parameter from the received control signal based on the judgment result. The electric generation control circuit controls the operation of the vehicle alternator based on the electric generation control parameter demodulated.