A conventional device for monitoring an appliance handles only gas usage and safety information at the time of gas shut off, and a social need for recognizing information about the impact of using a gas combustion appliance on the global environment (e.g. CO2 emission) was neglected. Based on a gas appliance used by a client and a gas flow rate signal thereof outputted from a section (2) for judging an appliance, and CO2 emissions data of the gas appliance stored in a CO2 emissions data storage section (3), a section (4) for calculating CO2 emissions operates CO2 emissions so that the client can determine CO2 emissions produced when the gas appliance is used.