PURPOSE: To shorten unavailable period due to replacement in such a way that new drop lifters which are divided to the left and right are moved along provisional guide rails, in the replacement of the drop lifters for overhead conveyor.

CONSTITUTION: New drop lifters 9 are assembled in the condition of being divided into left and right two units 10, 11, which are supported by means of provisional guide rails 5, 6 astride between (A) and B. When withdrawal operation of the existing drop lifters 3 are finished, the new units 10, 11 are moved to the existing position (A) as they are supported by means of the provisional guide rails. Then, the new drop lifters 9 are assembled using the both units 10, 11, and they are fixed with their upper and lower sides to a ceiling frame 7 and to the floor space 25. In consequence, the period can be widely shortened.