a multi - step focusing type electron gun is disclosed which includes a cathode , electrodes g1 and g2 , and electrodes g3 , g4 , g5 , g6 , g7 , and g8 for forming two unipotential auxiliary lenses and a bipotential major lens in the main lens , characterized in that the electrodes g4 , g5 , g6 , g7 are so constituted as to satisfy some specific formulas . the electron gun can reduce the size of the beam spot and the size of the halo formed around the beam spot . further the electron gun improves the spherical aberration , and provides the flexibility in designing for different purposes , as well as improving the image quality on the screen .