In a wind turbine generating apparatus, a heat generating device is provided inside the rotor head and has a hermetically-sealed structure from outside. A rotor head cooling air passage is formed through the periphery of the heat generating device to the inside of a wind turbine blade. A cooling air introduction portion through which cooling air flows and an air outlet from which the cooling air is discharged are provided in the rotor head cooling air passage to thereby form the air outlet in the wind turbine blade.