PURPOSE: To reduce the power consumption by a voltage dropping resistor by constituting the cathode substrate of the indirectly heated cathode of a fluorescent luminous device with a metal fine wire wound on an insulation- covered heater core wire and a bypass wire arranged along the heater longitudinal direction in contact with the metal fine wire.

CONSTITUTION: The heater section 3 of a fluorescent luminous device using in indirectly heated cathode is constituted with a tungsten wire 1 as a heater core wire and an alumina layer 2 as an insulating layer, an cathode substrate 6 made of a coil-shaped metal fine wire 4 and a linear metal bypass wire 5 reducing the resistance of the wire 4 is arranged on this layer 2. The bypass wire 5 of this substrate 6 is arranged along the longitudinal direction of the wire 1, the fine wire 4 is wound at the preset pitch on the bypass wire 5 and the heater section 3 so as to incorporate the bypass wire 5. The resistance of the substrate 6 of the indirectly heated cathode 20 is decreased to reduce the power consumption by a voltage dropping resistor.