Automotive alternator having detector for detecting initiation of rotation

An alternator (1) for use in an automotive vehicle includes a circuit for detecting initiation of rotation of an engine. Upon detecting the initiation of rotation, excitation current supply to a field winding (4) is started, and thereafter an alternator output is controlled by controlling the excitation current. A resistor (53) is connected to one phase winding (Y) of an armature to obtain a voltage indicating initiation of rotation during a period in which no excitation current is supplied to the field winding (4), and a capacitor (21) is connected to another phase winding (Z) to raise the indicating voltage level. Since the indicating voltage induced by a small amount of residual magnetism is increased to a sufficient level by the capacitor (21), the initiation of rotation can be accurately detected.