To obtain an excitation control system whose voltage detection characteristic is made identical to that of an excitation control device in another system when other installations incidental to a synchronous generator and the excitation control device are multiplexed by a method wherein the detection characteristic of a voltage detection part is changed in such a way that a voltage detection signal to be output by the voltage detection part and a reference value to be given from the outside become the same value.

In a voltage detection part 75, a reference value VS is input during the operation of a synchronous generator 1, and a detection characteristic is changed in such a way that a voltage detection signal VT and the reference value VS become the same value. As a result, when a correction instruction DM is input to a correction part 75B at the voltage detection part 75, the detection characteristic of the voltage detection part 75 is corrected so as to agree with the reference value VS. Thereby, the error, of the voltage detection signal VT, generated due to the accuracy of an instrument transformer 6 or the voltage detection part 75 is corrected, and the voltage detection signal VT and the reference value VS to be given from the outside can be made the same value. In addition, the correction instruction DM is input by the operation of a person in charge of the operation or the maintenance of an excitation control device 7.