PURPOSE: To prevent deformation of base metal while to increase electron emission substance applying area and to achieve long service life and high reliability by fixing a thin doughnut board and linear material on the base metal and fixing the base metal and cathode sleeve thereby providing electron emission substance layer on the base metal.

CONSTITUTION: A doughnut disc 32 is fixed on a base metal 33 then fixed through a disc 32 and welding point 35 near the end of base metal 33 to cathode sleeves 30, 30. Thereafter electron emission substance 34 is applied on the base metal 33. Since the distance between the sleeves 30, 30 and electron emission substance 34 is lengthened because of doughnut disc 32 placed between the base metal 33 and cathode sleeves 30, 30, influence of chromium contained in the sleeves 30, 30 can be reduced. Consequently electron emission substance 34 can be applied entirely on the face of beam metal 33. Thereafter a filament 31 is inserted to secure the sleeve on a heater supporting member to produce an electron gun structure.