To overcome the disadvantage of increase in total number of gas detectors and cost-up due to required installation of detectors for gases used for every monitoring point when detecting leakage of a plurality of types of gases.

The system mainly comprises high coherence gas detectors 2 installed in a plurality of monitoring points, sampling gas valves 5 for starting sampling of an environmental gas from the monitoring points when gas is detected and sending through sampling piping 3, one piece of detection piping 4 connected at the confluence of a plurality of sampling piping 3, and a plurality of gas detectors 6 for identification of gas type connected to the detection piping 4.