The invention relates to a device for supporting a platform (1A, 1B) that is used to lift loads or persons the height of a structure. Together with a platform (1A, 1B), the inventive device comprises winch-type platform-lifting elements (2, 3) and modular assemblable mast-forming elements (4, 6). According to the invention, each mast element (4, 6) is installed using the load platform (1A, 1B) which can be connected to the masts by means of: (i) the aforementioned winch-type lifting elements (2, 3) which can be disconnected at will from the masts, and (ii) means (5) for temporarily blocking the movement of the platform (1A, 1B) in relation to a modular element (4, 6) of each mast. In this way, when the movement of the platform (1A, 1B) is blocked, a modular element (4, 6) can be added to, or removed from the top of the masts in accordance with the desired platform (1A, 1B) lifting height. The invention is characterised in that the platform (1A, 1B) is positioned between two modular independent masts which form a lifting and guiding path (12), each mast having at least two guiding paths (11, 12) which are arranged in order to co-operate with a platform (1A, 1B), enabling the asynchronous movement of said platforms (1A, 1B).