The following paper describes a device in order to separate the inelastically scattered electrons from the electron diffraction pattern. By means of an electric and magnetic deflecting system the diffraction pattern is swept across the small entrance aperture of a filter lens. In this way an electron beam with a small divergence passes the filter lens. Behind the filter lens the electron beam is deflected by another deflection system, which is synchronised with the first. So one gets a diffraction pattern, the angular width of which is determined by the maximum deflection angle of the deflecting system. If the retarding potential of the filter lens is high enough, one can photograph the filtered electron diffraction pattern. By reducing the retarding potential one gets unfiltered diagrams.