To obtain a precise cathode body structure in which the dispersion of parallelism of a cathode substrate is small.

An opening in the upper part of a cathode sleeve 12 is blocked by press fitting and fixing such a cathode substrate 14 that electron-emitting material 13 is coated on its surface. On the outside of the cathode sleeve 12, a cathode-supporting cylinder 15 is arranged on the same axis, as it encloses the cathode sleeve 12, keeping a prescribed interval with the circumferential surface. Three small-diameter parts 16, having diameters smaller than the maximum diameter are formed on the upper part of the cathode-supporting cylinder 15, and inner surface sides of the parts are formed roughly flat. Weld margins 18, 19 are welded by laser both on the inner surface of the small-diameter parts 16 of the cathode-supporting cylinder 15 and on the circumference of the lower part of the cathode sleeve 12, and hereby the cathode sleeve 12 is held on the same axis, parallel to the cathode-supporting cylinder 15. A cathode body structure 11 is assembled with primary grid or the like by bonded glass, to thereby constitute an electron gun.