An image-forming device having, in an envelope, an electron-emitting element, an image-forming member for forming an image by irradiation of an electron beam emitted from the electron-emitting element, and an electroconductive supporting member for supporting the envelope. The potential of the supporting member is controlled to not be higher than the maximum potential applied to the electron-emitting element. The electron-emitting element and the image-forming member can be placed in juxtaposition on the same substrate, an electro-conductive substrate can be additionally provided in opposition to the face of the substrate, and the supporting member can be connected electrically to one of the electrodes and also to the electro-conductive substrate.