electron gun in a color cathode ray tube including a separate plate electrode having a thickness thicker than a focusing electrode or an anode , a smooth outer circumference of a rim part , and single electron beam pass through hole for passing of three electron beam in common each fitted to opposite edges of the focusing electrode and the anode , thereby preventing deformation of the plate electrodes , enlarging diameters of the electron beam pass through holes , to allow formation of accurate large sized main focusing electrostatic lens , improving focusing onto a screen , and preventing occurrence of discharge between the focusing electrode and the anode .