Disclosed is a formwork element (1) which can be assembled with other formwork elements (1) so as to form a formwork structure. A formwork shell (4) having an adjustable curvature is supported by means of back supports (5) so as to create a stiff formwork element (1) that sustains concreting pressure. The supports (5) have a preferably trapezoidal cross section and are provided with fastening flanges (6) on the edges thereof and at least one girder (7) that is located at a distance from the formwork shell (4). The length of the girder (7) is adjustable in order to set or modify the curvature of the formwork shell (4) which is made of steel or plastic. Intermediate pieces (9) are disposed between the fastening flanges (6) of the supports (5) and the formwork shell (4). The fastening flanges (6) are fixed to said intermediate pieces (9) so as to be pivotable or tiltable relative thereto about the longitudinal direction thereof. The cross section of the flanges and/or the intermediate pieces (9,12) having a convex shape or being provided with slopes (61).
