An electron gun is provided, in which a capacitance between a cathode and other electrodes, especially a control electrode is reduced largely without substantially changing a structure for supporting the cathode with an insulator. The cathode of this electron gun is disposed inside of the cylindrical metal shell. The cathode and the cylindrical metal shell are connected by three metal tabs. The cylindrical metal shell fits into a hole formed in the center portion of the insulator, and a metal outer frame is attached to the periphery of the insulator. The metal outer frame is welded to the inner surface of a cathode metal support. There is a control electrode facing the electron emitting surface of the cathode at a predetermined distance. Plural electrodes including an accelerating electrode are disposed in turn beyond the control electrode. Peripheries of the cathode metal support, control electrode, an accelerating electrode and other electrodes are embedded into sides of a pair of supporting rods that extend axially, so that the electrodes are fixed with a predetermined space between the electrodes.