Abstract: Apparatus for supporting a form member extending perpendicularly to the longitudinal axis of a form carrier, in particular for supporting the side face of a truss form for concrete. The apparatus has a support frame and a clamping device connected to the support frame. A tightening device and a holding member are arranged in such a manner in a knuckle joint arrangement that, upon tightening, a prestressing path for the apparatus along the form carrier, and, thus a prestressing force perpendicular to the plane of the side face, ensues so that the gap between the side face and the base plate remains sealed in a reliable manner despite the concrete pressure, which arises. In a preferred embodiment, the truss holder is provided with an adjustable carrier adjustable in height, and which can be adapted to the required truss height.