A fall protection device for a user working on horizontal surfaces in construction sites, which can adopt two end positions: an operating protection position and a non-operating storage position. The device has a mast releasably couplable at the lower end to a fixed element of the construction with the possibility of pivoting on its own vertical shaft; an arm at a first end of an articulated joint articulated with the end of the upper portion of the mast, the second end thereof being free and the arm configured to receive in an area of the second end the coupling of fastening and attachment for the user; a strut with a first end articulately joined to the arm and with a second end to be fastened on a point of the upper portion of the mast under the end of the upper portion where the mast is articulated with the arm.