A nanocrystal diamond film characterized by comprising as a main component a nanocrystal diamond of 1 to less than 1000 nm crystal grain diameter synthesized on a base material. This nanocrystal diamond film is formed on a base material outside plasma region in accordance with the plasma CVD technique using a raw gas containing hydrocarbons and hydrogen. This nanocrystal diamond film is used in anelectrochemical device, an electrochemical electrode, a DNA chip, an organic electroluminescent element, an organic electrophotoreceptive element, an organic thin-film transistor, a cold electron emitting element, a fuel cell and a catalyst.