PURPOSE: To miniaturize the constitution of the electric circuit of a neon tube, to reduce a setting space and to secure safety for the damage of the neon tube and to prevent the fault of an internal circuit due to the damage.

CONSTITUTION: This device is provided with a pulse trans 6 applying high voltage to the electrode 4 of the neon tube 1, a pulse sending part 5 sending a high frequency pulse signal to the pulse trans 6 and a protection means 7 stopping the sending of the high frequency pulse signal from the pulse sending part 5 based on a signal from a damage detection part detecting that the tubed part 2 of the neon tube 1 is damaged. Then, by the protection means 7, the damage of the neon tube 1 is detected based on the change of output voltage or output current from the pulse transformer 6 or the change of input current to the pulse transformer 6.