DEVICE PROVIDED WITH FIELD EMISSION TYPE ELECTRON GUN

PURPOSE:To reduce a variation in a detecting current even when the lead voltage and accelerating voltage of a field emission electron are largely altered as well as to make a detecting effect improvable, by structuring a device to minimize the variation of an electron flow jumping into a detector in a way of bringing the detector for emission current variations close to the side of an anode. CONSTITUTION:In case of a device provided with a detecting way for both of a field emission type electron gun and a field emission current, an anode surface 3 is set down as a reference, and when a distance of up to a virtual electrode source is set to S while a distance of up to a current detection angle limiting stop 6 to l1 and a distance of up to this stop 6 and a current variation detector 7 to l2 respectively, the electron gun is situated in a position that is set to l1