PURPOSE: To obtain an ionic current with a high luminance by surrounding a pin-like emitter with a gas introducing member which concentrates gas onto the extreme end of the said emitter.

CONSTITUTION: An insulating base 1 is provided with a penetrating hole 5, which is located close to a pin-like emitter 2 and into which a gas introducing pipe 8 is fitted. In addition, a cylinder-like gas introducing member 10 is provided so that it surrounds the emitter 2. Owing to the above constitution, since gas introduced from the pipe 8 flows through the member 10 onto the extreme end of the emitter 2, the gas having an improved concentration is ionized by a high- field area at or around the extreme end of the emitter 2, and thus produced ions are discharged through an aperture 4 of a drawer-type electrode 3. As a result, an ionic current with a high luminance can be obtained without disturbing the electric field deviloping around the emitter 2.