A cathode (5) for emitting photoelectrons or secondary electrons comprises a nickel electrode substrate (5c) with an aluminum layer (5b) deposited on it; an intermediate layer (5a) consisting of carbon nanotubes formed on the aluminum layer; and an alkaline metal layer (5d) formed on the intermediate layer (5a) and composed, for example, of particles of an alkali antimony compound that either emits photoelectrons in response to incident light or emits secondary electrons in response to incident electrons. The decrease in defect density of the particles reduces the probability of recombination of electron and hole remarkably, thus increasing quantum efficiency.