A rotor having a plurality of wind turbine blades, a generator to be driven by rotation of the rotor, a pitch angle controller for controlling a pitch angle of the wind turbine blades according to a speed of a generator, and a comparing and selecting section are provided. When the voltage of the utility grid is a predetermined value or less, the pitch angle controller controls the pitch angle so that the wind turbine blades do not move to a fine side. Further, the comparing and selecting section compares a temporary pitch angle command value determined based on the speed of the generator with a previous value of a pitch angle command value, and when the temporary pitch angle command value is a command for controlling the wind turbine blades closer to the fine side than the previous value, outputs the previous value as a current pitch angle command value.