A formwork system is provided for constructing a structural concrete floor, said formwork systems constitutes a main frame (100) forming a concrete slab structure, a plurality of side frames (110) each movably mounted at the edge of the main frame (100) for forming a concrete beam formwork structure, and a plurality of retainers mounted at the edge of the main frame (100) for supporting below the side frames (110) and jacking means for raising and lowering the formwork system. The side frame (110) being movable enables the formwork system to be effectively detached from a casted structural floor having concrete beams extended therefrom. The formwork system is also extricable on site after fabrication of the concrete ceiling slab floor and concrete beam.