provided is a field emission device using carbon nanotubes . the field emission device includes a substrate , a cathode , a gate insulating layer , an electron emitter , and a gate electrode . the cathode is formed on the substrate . the gate insulating layer is formed on the cathode and has a well exposing a portion of the cathode . the electron emitter is formed on the exposed portion of the cathode . the gate electrode is formed on the gate insulating layer and has a gate hole corresponding to the well . the gate electrode further includes a cylindrical electrode part that forms a focusing electric field from the gate hole toward a proceeding path of an electron beam . accordingly , a focusing electric field can be formed around an electron beam emitted from the electron emitter so as to converge and focus the electron beam passing through the focusing electric field . as a result , color purity , brightness , and durability can be improved .