By applying a drive voltage Vf [V] between first and second conductive
films, when electrons are emitted by the first conductive film, an
equipotential line of 0.5 Vf [V] is inclined toward the first conductive
film, rather than toward the second conductive film, in the vicinity of
the electron emitting portion of the first conductive film, in a cross
section extending across the electron emitting portion and the portion of
the second conductive film located nearest the electron emitting portion.
The present invention improves electron emission efficiency.