To provide a element having practicality capable of sufficiently emitting electrons even by a low voltage application in the use as a cold cathode element by constituting the element from an evaporation film containing Cs and providing a plurality of projections consisting of Cs oxide on the film surface.

A cathode unit 1 is formed of an Al cathode plate 2 and a cold cathode element 3 as an electronic element formed on the surface thereof. The cold cathode element 3 is formed of an evaporation film containing Cs, and it has a plurality of extremely fine conical projections(p) consisting of Cs oxide on the surface. The evaporation film, for example, is formed of an amorphous carbon film, and an average height(h) of each conical projection (p is set to 10 nm≤h≤500 nm. The active Cs on the film surface is combined with the oxygen in air to form a stable Cs oxide, and this Cs oxide forms the conical projections(p). Furthermore, the Cs within the film reduces the work function of C. Accordingly, even if the voltage applied to the cold cathode element 3 is reduced, a sufficient electron emission can be materialized.