PURPOSE: To predict deterioration of any component before visual judement become practicable.

CONSTITUTION: An operation counting part 1 counts the operating time for each eliminating area, while a controls counting part 2 counts and stores the frequency of on/off controls for each illuminating are. A reference value setting part 4 accommodates the respective reference values for different area for the operating time and the frequency of controls. A comparative control part 3 compares the current values of the operating time counting part 1 and the controls counting part 2 with their reference values accommodated in the reference value setting part 4. Judgement of deterioration in the illuminance is made on the basis of the given operating time and the frequency of on/off controls, and if either value exceeds its reference value, an alarm signal of deterioration of the applicable component is sent to an alarm issuing part 5. The alarm issuing part 5 gives a warning to the outside with alarm signal.