PURPOSE: To provide a cathode of a high-frequency radio wave generator which can reduce the unnecessary electron emission.

CONSTITUTION: While a nose 7 and a skirt 8 are provided concentrically on both side surfaces of an emission belt 6 through a clearance, a spacer 11 to combine the nose 7 and the skirt 8 is provided penetrating the center hole 6a of the emission belt 6 while making the spacer 11 not contact with the emission belt 6, and the emission belt 6 is held by a shield 10. And the unnecessary electron emission is suppressed, the purity of the oscillation mode is improved, and furthermore, no damage of the device is generated, and the electric power of a heater can be reduced.