The purpose of the present invention is to reliably contribute to the frequency recovery of a power system while avoiding the power output of a wind power generator from becoming cutoff when the frequency of the power system drops. Provided is a wind power generator for calculating a limit effective power on the basis of the difference between the measured value of a shaft rotation number and a predetermined rotation number lower limit value having a predetermined margin over the disconnection rotation number and for generating an effective power command value on the basis of the aforementioned limit effective power when a predetermined frequency drop occurred which requires the recovery of the frequency drop in the power system.