PURPOSE: To suppress the variations in the output voltage and rotational speed of a variable-speed generator and constant-speed generator by regulating the gain value of the transfer function of a command value generation means according to whether the variable-speed generator, provided with a stabilizing control system to suppress the variations in the output power of a constant-speed generator, is supplying power to a power system.

CONSTITUTION: A judging device 41 judges whether a variable-speed generator 10 is supplying power to a power system 1 by checking whether a breaker 11 is turned on or off. A gain setting device 42 adjusts the gain value of the transfer function in a command generation circuit of a stabilizing control system 7 according to the results of judgment by the judging device 41. When the judging device 41 judges that the variable-speed generator 10 is supplying power to the power system 1 by detecting on/off of the breaker 11, the gain setting device 42 resets the gain value of the transfer function in the command generation circuit of the stabilizing control system 7 smaller than it is, e.g. from 0.3 to 0.1., thereby suppressing the variations in the output and rotational speed of a constant-speed generator 3 and variable-speed generator 10.