An object 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. A diamond electron emission cathode according to the present invention has single crystal diamond in at least part thereof, the diamond electron emission cathode having a columnar shape formed by a sharpened acute section and a heating section, being provided with one electron emitting portion in the sharpened acute section, and being constituted of at least two types of semiconductors that differ in electric properties. One of the types constituting the semiconductors is an n-type semiconductor containing n-type impurities at 2.times.10.sup.15 cm.sup.3 or higher, the other one is a p-type semiconductor containing p-type impurities at 2.times.10.sup.15 cm.sup.-3 or higher, the p-type semiconductor and the n-type semiconductor are joined together, the heating section is energized parallel to the junction surface and directly heated by a pair of current introducing terminals, and some of the introduced electrons are emitted from the electron emitting portion.