A wind turbine generator having a large opening area for air intake and exhaust while maintaining tower strength and having a sufficient cooling performance is provided. In the wind turbine generator, a rotor head rotating when receiving wind power with wind turbine blades drives a generating machine provided inside a nacelle to generate electric power. The nacelle is provided on an upper end portion of a tower standing upright on a foundation. Outer air is introduced into the tower from a tower opening provided on a surface of the tower to cool an inner space of the tower. The wind turbine generator includes a recessed cylindrical portion extending from the tower opening toward the inner side of the tower. Air can pass through pressure loss elements provided on a part or all of a surface making up the cylindrical portion, and an effective opening area where the pressure loss elements are provided is larger than an actual opening area of the tower opening.