An in-line type electron gun using a field superimposing type main lens
system is provided that can attain good focusing properties by decreasing
the size of the electron beam spot on the entire surface of the phosphor
screen without being formed to be mechanically large. A field
superimposing type main lens is formed by disposing two tubular
electrodes opposite to each other and disposing a plate-like field
correction electrode on each of the tubular electrodes on the sides not
opposite to each other. On each of the opposite sides of the two tubular
electrodes, an opening is formed by an edge portion and a folded portion.
The shape of the opening may be an elongated flat-sided oval shaped
aperture (laterally elongated aperture) that is formed by straight lines
and semicircles and has a major diameter in the horizontal direction and
a minor diameter in the vertical direction. The in-line type electron gun
is configured such that a relationship B