A wind power generator system includes a windmill rotor including a blade whose pitch angle is variable; a generator driven by the windmill rotor; and a control unit controlling output power of the generator and the pitch angle of the blade. The control unit performs a first control in which the output power is controlled in accordance with a predetermined power-rotational speed curve until the rotational speed is increased to reach a predetermined rated rotational speed, and a second control in which the output power is controlled to a predetermined rated power when the rotational speed exceeds the rated rotational speed. The control unit is responsive to the pitch angle for maintaining the second control or for switching to the first control, when the rotational speed is reduced below the rated rotational speed after the control unit is once placed into the state of performing the second control.