PURPOSE: To hold data in a storage element for a certain period and dissolve the turnoff of a discharge lamp due to instant break by stopping the operation of a lighting circuit before the power voltage of the storage element is less than operation guarantee voltage when a power supply has instant break.

CONSTITUTION: When a power supply 1 has instant break during operating a lighting circuit 4, the output voltage of a rectification smoothing circuit 2 is discharged with the lighting circuit 4 as load. At this time, the power voltage VCC of a storage element 8 is made into constant voltage by a Zener diode 9, but it begins to drop because a transistor 11 is ON. Then, the Zener diode 9 is inserted into the output terminal of the storage element 8 to set Zener voltage higher than the minimum guarantee voltage of the storage element 8. It is thus possible to prevent data breakdown in short-time instant break and provide high reliability.