PURPOSE: To prevent breakage caused by a drop of a raisinglowering mechanism by giving an alarm when looseness of a turing mechanism is detected beforehand, and arranging a drop preventive plate.

CONSTITUTION: A raising-lowering mechanism 1 is suspended from the ceiling through a turning mechanism 2 and a fixed pole 3, and a fastening nut 27 is arranged in a lower part of a fixed side shaft 5 so that the turning mechanism 2 is not loosened, and a drop of the raising-lowering mechanism 1 is prevented. A drop preventive plate 28 is fixed the lower part of the fixed side shaft 25 by a bolt 29, and a looseness detecting switch 30 is installed, so that even if the fastening nut 27 to fasten the turning mechanism 2 is loosened, the looseness detecting switch 30 is operated in the first place and informs abnormality by outputting a detecting signal. When the looseness detecting switch 30 runs into trouble, or when the fastening nut 27 is loosened and disconnected completely until maintenance and inspection are carried out after the abnormality is alarmed, a bracket 26 is supported with the drop preventive plate 28, so that a drop of the raising-lowering mechanism 1 can be prevented. In this way, a safety measure of two stages is adopted.