PURPOSE: To unify sensors to improve economical efficiency by setting a sensor along a main oil feeding pipe and adjacently to the pipe and setting also other sensors along branched oil feeding pipes and adjacently to the pipe.

CONSTITUTION: A main oil feeding pipe 3A coupled with an oil tank is horizontally laid under the ground and branched oil feeding pipes 3B proportional to the number of oil feeding devices are branched from the main oil feeding pipe 3A so as to be vertically laid under the ground. In the setting method of oil leakage sensors, these sensors are economically unified, and if a sensor for the main oil feeding pipe 3A or a branched oil feeding pipe is broken, only the broken part can be replaced.