<p>An electron gun with a truncated-cone-shaped cathode with uniform emission current density is efficiently manufactured. A manufacturing method of a cathode electron gun equipped with a supply source for diffusing oxide of a metal element on a single crystal needle of tungsten or molybdenum includes steps of forming a truncated-cone-shape having a flat plane at a single crystal edge serving as the cathode by machining beforehand, thereafter thinning and removing a front layer of the flat plane by a focused gallium ion beam, and re-flattening it.</p>
