An object of the present invention is to provide an electron emission cathode and an electron emission source using diamond and having a high brightness and a small energy width that are suitable for electron ray and electron beam devices and vacuum tubes, in particular, electron microscopes and electron beam exposure devices, and also electronic devices using such cathode and source. The diamond electron emission cathode according to the present invention has single crystal diamond in at least part thereof. The diamond electron emission cathode has a columnar shape having a sharpened acute section and a heating section. One electron emitting portion is provided in the sharpened acute section. The electron emitting portion and heating section comprise a diamond semiconductor. The diamond semiconductor is a p-type semiconductor having p-type impurities at 2×1015 cm−3 or higher. The semiconductor is present in the electron emitting portion. A metal layer is formed on the surface of the electron emission cathode. The metal layer is present in at least part of the heating section. The shortest distance from the electron emitting portion to an end portion of the metal layer is 500 μm or less. An electric current for heating is supplied to the heating section with a pair of current introducing terminals, and some of the introduced electrons can be emitted from the electron emitting portion.