To start of rotation of a windmill by only wind force without necessitating other starting means by connecting a shaft which is disposed in parallel with a main shaft of the windmill in blades for receiving wind, to a wind receiving plate disposed adjacently to the blades by power transmitting means, in a vertical shaft windmill having a rotary shaft which is disposed perpendicularly to wind.

A vertical shaft windmill has a pair of blades 3 disposed symmetrically to a main shaft 1, the both blades 3 are supported around the main shat 1 freely to turn by upper and lower arms 2a, 2b. A gear 6 is fixed to an upper end of each blade 3, a gear 8 is fixed to a shaft 10 of a dog vane plate 4 disposed on a tip end of a bending part of each end of the arm 2a, and the gears 6, 8 are interlocked with each other through a belt 9. Namely, when an angle of the dog vane plate 4 is changed by receiving wind force, the blade 3 is interlocked so as to rotate at only a half-angle in the rotational direction, the blade 3 is rotated so as to receive wind at a proper angle at all times, and the main shaft 1 is rotated by turning of the blade 3 receiving wind.