To provide an energy source for a secondary battery which can eliminate the disadvantages in a secondary battery charging system of an electric vehicle, including (a) a secondary battery must be charged back in a garage or a base before it runs out of capacity, (b) the total weight of a vehicle including a secondary battery becomes large, and (c) the expansion of the charging facility is indispensable.

The surface of a bonnet of an electric vehicle is provided with a duct 2 for taking in wind pressure/air flow. Wind 4 blown out from a port of the duct 3 located inside the bonnet rotates vanes 5 of a wind power generator to rotate a power generator 6 directly connected to the rotating vanes and take out power. The electric power energy taken out is converted to 24 V or 12 V by means of a charger 7 and is supplied to a secondary battery 8. Thus, the secondary battery 8 can be continuously charged.