Abstract: An over-drive gear device for use with a wind generator of a windmill, which includes a bevel gear member connected to a rotary shaft of the windmill, first and second vertical axle shafts extending from the bevel gear, an internal gear member connected to the second vertical axle shaft, a planet gear spider connected to the first vertical axle shaft and including a plurality of planet gears, and a sun gear disposed in a geared relationship with the plurality of auxiliary gears, wherein the wind generator is coaxially connected to the main gear and the over-drive gear device effectively increases the total efficiency of the wind generator of the propeller-type windmill.