PURPOSE: To enable high current density operation and low temp. operation by supplying barium atoms from the lower part of a surface thin film layer, and specifying the area of the region to be supplied from the part directly under.

CONSTITUTION: A surface thin film layer 2 is formed on the over-surface of a thick film layer 2, and besides tungsten the thin film layer 3 contains at least scandium or its oxide. Barium atoms are supplied from below the thin film layer 3, and a barium supplying body is provided in which the area of the region supplied with barium atoms occupies not less than 50% of the area of the region utilizing electrons emitted from the surface of a facial covering film layer. A base board 1 of high melting point metal is used a disc having a recess in the center, and the thin film layer 3 and base board 1 are connected electrically at the periphery of the disc. Accordingly barium is supplied to the thin film layer 3 uniformly in a large quantity to generate good electron emission, and temp. rise in the neighborhood of a cathode can be suppressed. It is also possible to make low temp. operation which enables large current density operation, to lead to enhancement of the reliability.