It is possible to provide an electron emission cathode, an electron emission source having a high-luminance and narrow energy width by using diamond and an electronic device using them. The diamond electron discharge cathode has a monocrystal diamond at least at a part of it. The diamond electron emission cathode has a columnar shape including a sharpened section and a heating section. The sharpened section has an electron emission section. The electron emission section and the heating section are formed by diamond semiconductor, which is formed by a p-type semiconductor containing 2×1015 cm−3 of p-type impurities or above. The electron emission section has the semiconductor. A metal layer is formed on the surface of the electron emission cathode. The metal layer exists at least at a part of the heating section. The distance from the electron emission section to the position nearest to the end of the metal layer is 500 μm. A pair of current introduction terminals supplies current to the heating section to heat the heating section. A part of the introduced electrons is emitted from the electron emission section.