An apparatus for the manufacturing of a formwork member comprising a first formwork panel made of expanded polystyrene, by a plurality of truss metal structures arranged parallel to one another, said apparatus comprising a feeding station configured to feed along a manufacturing direction a plurality of truss metal structures arranged in parallel and a molding station arranged after said feeding station and configured to receive therefrom said truss metal structures along said manufacturing direction and to make on a portion thereof a first panel of a formwork member, wherein said molding station comprises a molding chamber configured for the injection of polystyrene spheres or beads and their expansion by supplying steam, said spheres or beads being intended to form said first panel embedding a portion of the truss metal structures, and wherein said molding station also comprises a dimensional stabilization chamber contiguous to said molding chamber and configured to receive the first panel formed therein, the apparatus further comprising a moving assembly arranged directly after the molding station, said moving assembly being configured to grab a portion of the first panel coming out from the dimensional stabilization chamber and make it move in the manufacturing direction by a desired length, characterized in that the formwork member further comprising a second formwork panel made of expanded polystyrene, said first and second formwork panels being restrained and spaced apart from each other by the plurality of truss metal structures, and an auxiliary molding chamber is arranged between the molding chamber and the dimensional stabilization chamber, said auxiliary molding chamber communicating with the molding chamber and the dimensional stabilization chamber, and in that the auxiliary molding chamber is configured to be selectively heated by supplying steam. wherein said molding station comprises a molding chamber configured for the injection of polystyrene spheres or beads and their expansion by supplying steam, said spheres or beads being intended to form said first panel embedding a portion of the truss metal structures, and wherein said molding station also comprises a dimensional stabilization chamber contiguous to said molding chamber and configured to receive the first panel formed therein, the apparatus further comprising a moving assembly arranged directly after the molding station, said moving assembly being configured to grab a portion of the first panel coming out from the dimensional stabilization chamber and make it move in the manufacturing direction by a desired length, characterized in that the formwork member further comprising a second formwork panel made of expanded polystyrene, said first and second formwork panels being restrained and spaced apart from each other by the plurality of truss metal structures, and an auxiliary molding chamber is arranged between the molding chamber and the dimensional stabilization chamber, said auxiliary molding chamber communicating with the molding chamber and the dimensional stabilization chamber, and in that the auxiliary molding chamber is configured to be selectively heated by supplying steam.