PURPOSE: To make it hard to decrease the electron emitting function of a cathode and to decrease the quantity of light by installing a shutting means between a cathode to which an emitter is applied and an anode in which a phosphor is densely.

CONSTITUTION: A phosphor body 70 is applied to the inner side of a front plate 36 of a light emitting tube 34 and an anode 72 coated with Al by vaccum evaporation is installed on it. A back side electrode 40 is formed in the inside of a back side plate 38 by vacuum evaporartion of Al. A cathode 74 is set above the electrode 40. An emitter 76 is applied to the surface of the cathode 74 made of W. A grid 60 is installed between the cathode 74 and the anode 72. Voltage is applied to the cathode 74 to heat it and at the same time high voltage is applied to the anode 72. A part of thermal electrons 26 emitted from the cathode 74 are captured by a shutting means 46 in the center part of the grid 60. The rest of the thermal electrons 26 are rebounded by the electrode 40 to which negative voltage is applied, pass the open part 44 of the grid 60, come into collision against the anode 72, and cause fluorescence of the phosphor body 70. A part of the phosphor body 70 becomes flying bodies 30 by sputtering. The flying bodies 30 are shut by the means 46 and prevented from adhering to the cathode 40.