PURPOSE: To shorten wasteful time taken from application of power until starting of preheating, and shorten the starting time of an electric-discharge lamp by installing a quick-acting movable electrode, which is made of a bimetal, has a small heat capacity and has a high sensitivity, in such a manner that it faces to a fixed electrode, and connecting the quick-acting movable electrode to the terminal of a main movable electrode.

CONSTITUTION: A quick-acting movable electrode 6 is heated by designing the distance between the electrode 6 and a fixed electrode 1 and the like so that glow electric discharge develops between the electrodes 6 and 1. Since the electrode 6 has a small heat capacity and is a quick-acting electrode having a high sensitivity, it curves satisfactorily rapidly compared to the usual glow electric-discharge tube until the space formed between the electrodes 1 and 6 is closed. As a result, a current flows through a circuit consisting of a terminal 4, a heater 7, the electrode 6 and the electrode 1, and heats the heater 7. Then, a main movable electrode 2 made of a bimetal is heated and immediately curved, the space formed between the common electrode 1 and the electrode 2 is closed, and a preheating current flows between a terminal 3 and the terminal 4. Consequently, the starting time of an electric-discharge lamp can be shortened by decreasing wasteful time taken until the preheating current begins to flow.