mgag film with a thickness of 50 nm or less preferably 20 nm alloy film formed by evaporating magnesium and silver and the transparent electrode 1604 b that is a conductive oxide film thickness 200 nm formed by adding gallium oxide to zinc oxide the protecting film 1605 that is formed using a dlc film is stacked on the cathode 1604 after a light emitting element is formed to have any one of the constructions described above the light emitting element is sealed and dlc films are formed at end portions with any one of the aforementioned methods in this manner the degradation due to oxygen and moisture is prevented in this embodiment the cathode of a light emitting element is formed with a method differing from that of embodiment 1 here the method of forming a cathode is below described with reference to fig1 a and 17b in fig1 a a cathode 1702 made of an alkaline metal li or mg for instance with a low work function is formed on an insulating film 1701 then an organic compound layer 1703 an anode 1704 and a protecting layer 1705 a dlc film are formed on the cathode 1702 in fig1 b a transparent electrode 1702 a that is a transparent conductive film ito and a translucent electrode 1702 b that is an ultra thin thickness 50 nm or less metal film al u2014 li alloy film or mg alloy film for instance are stacked in this order on the insulating film 1701 to form the cathode 1702 then the organic compound.