A device for measuring the filling level of a fuel tank, in particular for motor vehicles, having two openings for installation of a filling connection and a pump unit, and a film sensor provided with an electric connecting cable which can be connected to a display device through the pump unit. The film sensor is embedded in a protective tube which is provided with inlet openings for the fuel. The protective tube is mounted on the filling connection at the side and can be inserted jointly with it into the respective opening in the fuel tank.