To form a completely round beam spot on a fluorescent screen and to improve resolution by forming the aperture of the electrode of an electron beam driving system on the cathode side than a main lens system electrode of an electron gun into an ellipse.

The electrode of an electron beam driving system for extracting an electron beam from a cathode K, e.g. first and second grids G1, G2, is formed into a bottomed cylindrical shape, an aperture 16 is bored at the center position of the bottom in an oblong elliptic shape, thereby the prescribed electrode of an electron gun is made astigmatic, and the magnifying power of an image in the Y-axis direction can be reduced. No electric control is required for making an electron beam astigmatic by merely forming the aperture 16 of the electrode of the electron beam driving system such as the first grid G1 or/and the second grid G2 into the oblong elliptic shape. An oblong elliptic spot 17 is formed on a virtual vertical plane 13, however a completely round spot 18 is obtained on an inclined fluorescent plane 5 due to astigmatism, and resolution can be improved.