To provide a thunderbolt protective device of a wind power generator superior in the facility volume, cost and safety.

This wind power generator has structure for driving a generator by a blade rotatingly driven by wind by arranging the blade journaled in the substantially horizontal direction to the ground surface in a nacelle arranged in a tower top part. A thunder approach detecting device 1 detects the approach of a thunder. A stopping device 2 stops the highest part among the blade 3 in a rotational position lowest from the ground surface by detecting the approach of a thundercloud, and holds the part in this rotational position, and reduces a thunderbolt by putting the blade in a thunderbolt hardly falling state and an attitude when the thundercloud approaches. The thunder approach detecting device is composed of a corona discharge detecting device or an electric field strength detecting device, arranged in the vicinity of a discharge gap in a lightening arresting passage reaching the nacelle from the blade, and detects the approach of the thunder by an increase in corona discharge or electric field strength when a thunder approaches.