To provide a generator control system which enables reduction of the number of connecting wires necessary when a plurality of signals are transmitted from a generator to an external controller, reduction of the weight and cost, enhancement of the workability and reliability, and simplification of its configuration.

A generator 1 for vehicles which has a built-in power generation controller 2, a battery 3, and an external controller 5 are connected into a closed loop via a control route. Via this control route, signal F representing the state of the exciting current of the generator 1 and signal L representing the operating state of the generator 1 are transmitted between the generator 1 and the external controller 5.