PURPOSE: To convert gentle wind power into electrical power in safety by transforming wind pressure into reciprocating motion which is transmitted to a coil disposed in magnetic field.

CONSTITUTION: Wind pressure exerted into a box 1 pushes a back plate 4 under its pressure in the direction of A. Simultaneously, pressure in the box 1 is lowered since a gap is formed between the box and the back plate 4, thereby the back plate 4 is returned to its original position by force of a spring 3 so as to close the gap. When the back plate abuts against the box 1, pressure in the box again increases. Since the above motion is successively repeated, the back plate 4 is reciprocated. The back plate 4 carries thereon an iron core 40 and a coil 6 which receives or is surrounded by yorks 7 and which is disposed in magnetic field established by a magnet 8. Accordingly, when the coil 6 is reciprocated by wind pressure, alternating current electrical power can be obtained at terminals 9.