A wind turbine generator is provided in which, even in a cold snowy environment in a cold region, the time required for recovering a frozen anemoscope/anemometer is reduced to minimize a decrease in operating ratio. A wind turbine generator is equipped with an anemoscope/anemometer (7) at the top of a nacelle that accommodates a driving and generating mechanism connected to a rotor head on which turbine blades are mounted, wherein an in-nacelle cooling air outlet that opens in the direction of the anemoscope/anemometer (7) is provided at the top of the nacelle, and the air outlet has exhaust flaps (13) serving as blowing-direction changing means for the cooling air.