To provide an efficient wind power generator which is always rotated by only effective force without letting negative force act on a blade, though the negative force is always acting on the blade which is a rotation part in the direction opposite to the rotation direction, when a vertical cross-flow type wind power generator is rotated by receiving wind; to provide a device with a wind receiving area of an effectively-working part enlarged to the maximum, as an amount of power generation work is proportional to the wind receiving area.

The negative force which becomes resistance when the rotation blade moves is not allowed to act on the blade by providing an air volume adjusting guide for covering the blade. In addition, as a position of a tip plate of the guide contacts a rotation locus in a half-oval shape with the apex at around degrees from a rotation shaft as shown in Fig.2 so as to increase the effectively-working wind receiving area, the structure has an effect for letting the wind received by the tip plate flow to the rotation direction of the blade. By this effect, the part for originally receiving the negative force can be converted to the force effectively-working in the rotation direction.