A device for indicating the filling level of a container, including: a first mobile element located inside of the container and capable of moving along a wall of the container when the filling level of the container varies; an enclosure containing a liquid or a gel, located outside of the container on the side of said wall opposite to the first element; and a second mobile element located inside of the enclosure and plunged into said liquid or gel, the second element being magnetically coupled to the first element and being capable of moving in the enclosure along said wall by following the displacements of the first element.