Abstract: An electron gun with an improved structure for providing accurately adjusted cut-off voltage. A novel process for producing the improved electron gun, and maintain substantially high uniformity of cut-off voltge in production. The electron gun comprises a plurality of grid electrodes including a first electrode mounted at the closest position to a cathode. The cathode is supported by a cathode base. The cathode base and the first electrode are provided in a pre-assembled form. The pre-assembly of the cathode base and the first electrode is supported by means of a holder which is fixed to glass beads together with other grid electrodes. In assembling of the electron gun, the distance between the cathode surface of the cathode and a plane surface of the first grid electrode, where an electron beam path is defined, is precisely adjusted during formation of the pre-assembly.