Abstract: An electron emission element of the present invention comprises a substrate, and a protrusion protruding from the substrate and including boron-doped diamond. The protrusion comprises a columnar body. And a tip portion of the protrusion comprises an acicular body sticking out therefrom. The distance r [cm] between a center axis and a side face in the columnar body and the boron concentration Nb [cm−3] in the diamond satisfy the relationship represented by the following formula (1): 1 r > 10 4 Nb .

Abstract: A diamond electron emission element is provided with a substrate, and a plurality of quadrangular columns (microscopic projections) composed of diamond and with side faces of flat faces, which are arranged at equal intervals on the substrate. A top end face (horizontal section) is of a quadrangular shape having a length of long sides being a [nm] and a length of short sides being ka [nm], and a thin film of SiO2 is formed on a side face on the short-edge side. The length a [nm] of long sides and the length ka [nm] of short sides satisfy relational expressions of Formulae (1) and (2) below.