Abstract: A vertical type wind-driven prime mover comprises a vertically extending rotative main shaft, a plurality of horizontal support arms radially extending from the main shaft, a rectangular support frame body pivotally connected to the outer end of each of the arms, a rectangular wind receiving plate pivotally connected to each of the support frame bodies so that these plates are swingable only on the same one side of the respective support frame bodies, and a weight attached to each support frame body to maintain the latter substantially vertical until the wind speed reaches a given value.