A turbine controller of a wind turbine generator includes a generated-output-power command value creating section that creates a generated-output-power command value and an optimum-upper-and-lower-limit limiting section that limits the generated-output-power command value by means of an upper limit value and a lower limit value of the generated output power that are determined based on a power curve indicating the relationship between the generated output power and the rotational speed of the generator. Furthermore, the turbine controller includes a limit-value creating section that creates, when the grid frequency is increased above a predetermined reference frequency, a frequency-dependent limit value serving as an upper limit value of the generated-output-power command value, according to the increase in grid frequency; and a first upper-limit limiting section that limits the upper limit value of the generated-output-power command value limited by the optimum-upper-and-lower-limit limiting section, by means of the frequency-dependent limit value.