Abstract: A gas leakage detection system permits the detection of gas leakage within a field of a definite scope to be performed easily and reliably. The gas leakage detection system comprises: gas supply amount detection means (1) that detects the amount of gas supplied at the main side of a gas line that branches out to individual gas users, gas usage detection means (2) that detects the amount of gas used by each of said individual gas users, and leakage determination means (3) that finds the total amount of gas used as the sum of the amounts of gas used by the individual gas users, compares this total amount of gas used against the aforementioned amount of gas supplied, and thus determines whether or not there is any leakage of gas between the main side of the gas line and the individual gas users.