Abstract: A locking device of a flexible laminar element connected to a frame, in order to achieve a bearing structure which houses a person's body, comprises a groove obtained along one part of the perimeter of the frame and a shaped insert which is pressed into the groove in order to constrain the perimetral edge of the flexible laminar element between the groove and the shaped insert. Inside the grove a plurality of openings is arranged for the passage of as many appendixes of the shaped insert equipped with coupling elements which snap the shaped insert to the frame.