To provide a straight-line airfoil water/wind mill which has low resistance even when immersed into a stream of water, applies no excessive moment or a corrosive atmosphere to a rotary shaft, and which eliminates the need for separate installation of an anemometer, and also to provide a method of power generation using it.

In the water/windmill for power generation and the method of power generation using it, two or more horizontal straight-line wings are arranged on the circumference about a horizontal shaft. Then the two or more horizontal straight-line wings rotate about the horizontal shaft by lift generated when wind or a stream of water passes the circumference of the horizontal straight-line wings.