The structure of a concentrator mirror includes a prefabricated body of reinforced concrete, which includes a panel member having a front surface with a reflective laminar layer, and a back surface, between which a hinge axis for the rotation of the panel is defined. A pair of coaxial hollow seats are formed in the body at respective longitudinally spaced positions, to define the hinge axis together with respective spherical joints. The body includes a rib shaped counterweight appendage extending parallel to the hinge axis from the back surface of the panel member, on the side opposite the front surface, so as to bring the hinge axis in a barycentric position of the body.