A control apparatus for a vehicular alternator can improve its reliability and reduce its cost by attenuating a field current of a rotor coil with a simple circuit. The apparatus includes an armature coil, a rectifier circuit, a rotor coil and a voltage control circuit. The rectifier circuit has an AC input terminal, a positive and a negative output terminal. The voltage control circuit controls a generation voltage to be substantially constant by interrupting a field current when a generation voltage exceeds a first predetermined voltage, while passing the field current when the generation voltage is equal to or lower than the first predetermined voltage. A circulation circuit comprising a diode and a current attenuation element serves to circulate the field current upon interruption thereof. A short-circuiting circuit short-circuits the current attenuation element. A short-circuit control circuit opens the short-circuiting circuit when the generation voltage exceeds a second predetermined voltage.