A cathode includes a hairpin type filament made of a refractory metal such as W, Mo or Re; a single crystal needle, made of a refractory metal such as W, Mo or Re joined to the filament; and a reservoir formed by applying a slurry of a powder of a metal or metal compound and an organic solvent containing nitrocellulose in the vicinity of a junction between the single crystal needle and the filament. The powder for a reservoir is made of a metal lower than the single crystal needle in a work function or electron affinity, such as Ti, Zr, Hf, Y, Th, Sc or Se, or a compound thereof.