A blade comprises a first blade surface, a second blade surface forming the reverse surface of the first blade surface, a primary wind receptor protruding from the front end of the first blade surface in a direction away from the second blade surface and with the back surface formed in a curved shape concave toward the front side in a forward direction, a front edge connected to the front end of the primary wind receptor and the front end of the second blade surface and formed in a curved shape convex toward the forward direction, and a back edge connected to the back end of the first blade surface and the back end of the second blade surface and formed in an acute angle facing the back side of the forward direction.