A wind power generator (14) generates power through a rotation of a rotor (12) and is interconnected, and operated with its power generation output previously limited in order to be able to further supply the power to a power system (20) in response to a decrease in system frequency. Thus, a concentrated control system (16) derives a required restricted amount corresponding to a power generation output required to respond to the decrease in system frequency, derives a value by subtracting an amount corresponding to a latent power generation output with which the power generation output can be increased, from the required restricted amount, and sets a restricted amount of the power generation output in each wind power generator (14) to perform the operation with the power generation output previously limited to respond to the decrease in system frequency, based on the above value. Thus, even when the wind power generator (14) performs the operation with the power generation output limited, the restricted amount of the power generation can be small.
