A control apparatus for a vehicle electric generator judges the currently available generating capacity of the generator and establishes a regenerative current mode of operation, utilizing an induced current of the field winding, only when the generating capacity is estimated to be below a predetermined level. The control apparatus also controls the conduction factor of a power transistor to adjust the average voltage applied to the field winding such as to prevent fluctuations in output current and generator torque that would otherwise occur at each changeover to/from the regenerative current mode.