To reduce phenomena in which force applied to a wing instantaneously differs and rotation energy of a straight wing vertical shaft type wind mill fluctuates depending on amount of wind velocity fluctuation of natural wind by the arrangement of wings.

Length of the conventional wing is divided into small parts having length of 1/2 or more, these small parts are divided into upper and lower parts, and the wings are arranged by deviating positions of the wings from each other at each step. Consequently, since influence force of the wing received from natural wind differs depending on step, well-balanced rotation force is obtained on the whole and rotation of the wind mill is made smooth.