To prevent a generator from generating voltage higher than a set value even if wind speed increases and a blade rotates at high speed.

A rotor 19 provided with a magnet 20 is fixed on a windmill including a down blow style blade 18 rotating even receiving gentle wind as one unit. A spring gradually moving the windmill and the rotor 19 in a horizontal direction in relation to a rotary shaft to reduce degree of magnetic engagement with a stator coil 10 fixed on a body 4 when wind speed is set rotation speed or higher is included and power generation performance is controlled.