The purpose of the invention is to protect, in a horizontal axis wind turbine with an exhaust aperture for exhausting air from within the nacelle, the exhaust aperture and the internal structures from storm winds through facing the exhaust aperture away from the storm wind, even when storm winds are received from all directions relative to the nacelle. A rotary duct is attached to the nacelle so as to be able to rotate freely in the yaw direction, and is rotated in the yaw direction in accordance with changes in the wind direction. The exhaust aperture is provided at a position that changes direction depending on the rotation of the rotary duct in the yaw direction. By rotating the rotary duct in the yaw direction so that the exhaust aperture will face the downwind side in accordance with changes in the wind direction, the exhaust aperture can be faced away from storm winds, even when storm winds are received from all directions in relation to the nacelle.