PROBLEM TO BE SOLVED: To report a broken filament lamp airport separately from a local station abnormality without visiting a local station installation position and to shorten the recovery time. SOLUTION: A broken filament information request is held in the transmission signal including a transmission address section and a broken filament data section for individual local stations 91, 921, 941, 961, 981. When the local stations 91, 921, 941, 961, 981 receive the transmission signal and read the broken filament information request, the relevant local station 91 writes the broken filament lamp information of its own in the broken filament data section of the transmission signal, rewrites the transmission address section to other local stations 921, 941, 961, 981 or a transmission master station 51, and transmits the transmission signal.
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