The present invention relates to a charging generator control system comprising a generator which includes a field winding, and an armature winding being in three-phase connection to generate an A.C. output; a rectifier which rectifies the A.C. output from said armature winding of said generator; a battery which is charged with a D.C. output from said rectifier and which can supply an exciting current to said field winding; a separately-exciting power source which generates a D.C. voltage having a magnitude independent of the generator output and which can supply an exciting current to said field winding; a voltage regulator which controls the exciting current flowing through said field winding of said generator, thereby to control the output voltage of said generator to be a predetermined value; and a switching circuit which changes-over between said battery and said separately-exciting power source, depending upon a rotating speed of said generator, a condition of a load and a capacity of said separately-exciting power source as the exciting current sources of said field winding.