A wind turbine generator, an active damping method thereof, and a windmill tower in which vibrations of the wind turbine generator itself or the windmill tower can be reduced at low cost are provided. The acceleration due to vibrations of a nacelle (13) is detected with an accelerometer (17) attached to the nacelle (13). In an active damping unit (20), a pitch angle of windmill blades (12) for generating a thrust on the windmill blades (12) so as to cancel out the vibrations of the nacelle (13) is calculated on the basis of the acceleration, and the pitch angle is output as a blade-pitch-angle command ´¸* for damping. On the other hand, in a pitch-angle control unit (30), a pitch angle of the windmill blades (12) for controlling the output to be a predetermined value is calculated, and the pitch angle is output as a blade-pitch-angle command ¸* for output control. The blade-pitch-angle command ´¸* for damping is combined with the blade-pitch-angle command ¸* for output control using a subtracter (40). The pitch angle of the windmill blades is controlled on the basis of the resulting blade-pitch-angle command after combining.