Wind power generating equipment comprising: a generator that is driven by a blade which rotates by receiving the wind; a power converter configured to convert an electric output of the generator such that the output is interconnected with an electric power system; a power converter controller configured to control the power converter; a wind turbine control board configured to transmit an active power command value to an active-power calculating unit, which outputs a command value of the electric output which is transmitted from the power converter, and to an active-power-command-value storage unit of the power converter controller, characterized in that the active-power calculating unit is configured to output the active power command value transmitted from the wind turbine control board as said command value of the electric output during a normal operation state when a system voltage is normal, and the power converter controller is configured to control the electric output of the power converter in response to an active power command value that depends on a reduction amount of a system voltage during a voltage reduction state when instantaneous reduction occurs in the system voltage interconnected with the wind power generating equipment, wherein the active-power calculating unit is configured to output the active power command value that depends on a reduction amount of a system voltage as said command value of the electric output during the voltage reduction state, wherein the active-power-command-value storage unit is configured to save and store the active power command value received from the wind turbine control board and to output an active power command value obtained before one sampling, and, during the normal operation state, the active-power-command-value storage unit is configured to update the active power command value by repeating saving, storing and outputting of the active power command value, and, during the voltage reduction state, the active-power-command-value storage unit is configured to stop updating the active power command value and to store a final value obtained when the system voltage was in normal operation state, and a multiplier of the power converter controller is configured to compute and output to the active-power calculating unit the active power command value that depends on a reduction amount of a system voltage which is a product of a normalized system voltage value and the active power command value before one sampling received from the active-power-command-value storage unit. a generator that is driven by a blade which rotates by receiving the wind; a power converter configured to convert an electric output of the generator such that the output is interconnected with an electric power system; a power converter controller configured to control the power converter; a wind turbine control board configured to transmit an active power command value to an active-power calculating unit, which outputs a command value of the electric output which is transmitted from the power converter, and to an active-power-command-value storage unit of the power converter controller, characterized in that the active-power calculating unit is configured to output the active power command value transmitted from the wind turbine control board as said command value of the electric output during a normal operation state when a system voltage is normal, and the power converter controller is configured to control the electric output of the power converter in response to an active power command value that depends on a reduction amount of a system voltage during a voltage reduction state when instantaneous reduction occurs in the system voltage interconnected with the wind power generating equipment, wherein the active-power calculating unit is configured to output the active power command value that depends on a reduction amount of a system voltage as said command value of the electric output during the voltage reduction state, wherein the active-power-command-value storage unit is configured to save and store the active power command value received from the wind turbine control board and to output an active power command value obtained before one sampling, and, during the normal operation state, the active-power-command-value storage unit is configured to update the active power command value by repeating saving, storing and outputting of the active power command value, and, during the voltage reduction state, the active-power-command-value storage unit is configured to stop updating the active power command value and to store a final value obtained when the system voltage was in normal operation state, and a multiplier of the power converter controller is configured to compute and output to the active-power calculating unit the active power command value that depends on a reduction amount of a system voltage which is a product of a normalized system voltage value and the active power command value before one sampling received from the active-power-command-value storage unit.