A gas monitoring system and a gas monitoring method make it possible to identify plural gas sensors having a single specification and which are connected to one trunk line. Trunk line connectors have identification configurations for allowing information concerning positions where the trunk line connectors to be identified are arranged. Hydrogen sensors have a single specification (the same specification). When connectors of the hydrogen sensors are fitted to the trunk line connectors, the hydrogen sensors store the sensor IDs, which are assigned to the hydrogen sensors, in memory units based on the identification configurations of the trunk line connectors.