PURPOSE: To detect gas leakage in a common pipeline and a plurarity of individual pipelines branching off from the common pipeline so as to feed gas to each consumer, in course of feeding gas.

CONSTITUTION: A station meter 13 and each of consumer meters 141-14n send the information of flow rates in a common pipeline 11 and individual pipelines 121-12n to a processor 20 every specified time. A leakage judging part 22 of the processor 20 judges whether the value obtained by subtracting the sum of flow rates in the consumer meters 141-14n from the flow rate in the station meter 13 exceeds an allowable error, and judges no leakage in the case of not exceeding the allowable error while judging that there is leakage in the common pipeline 11 and individual pipelines 121-12n reaching the consumer meters 141-14n from the station meter 13 in the case of exceeding the allowable error.