Field emission electron gun

A field emission electron gun capable of generating a highly stabilized electron beam, comprises a cathode tip for emitting electrons, an anode for attracting and accelerating the electrons, and means for heating the anode. A surface layer of the anode, which is to be bombarded by the electrons, consists essentially of getter material such as Zr-Al alloy. The anode heating means serves for heating the surface layer, so as to remove the absorbed gas molecules and to elevate the gettering effect of the getter material, whereby the absorbed gas molecules in the anode are hardly released therefrom, even if the anode surface is bombarded by the electrons. Therefore, the number of ions impinging on the cathode tip is remarkably reduced, and a stable electron beam can be obtained from the cathode tip.