A convention appliance monitoring apparatus handles only the amount of gas used and security information for the case of a gas cutoff and can not address social needs for a desire to obtain information about influence (e.g., an amount of CO2 emission) of use of the gas combustion appliance on a terrestrial environment.Based on a gas appliance used by a client and a gas flow signal pertaining the gas appliance which are output from an appliance determination unit 2, CO2 emission data on the gas appliance stored in a CO2 emission data storage unit 3, and CO2 emission data which are to be compared with the gas appliance and stored in a comparative CO2 emission data storage unit 4, a CO2 emission calculation unit 5 calculates an amount of CO2 emission, an comparative amount of CO2 emission and a difference between the amount of CO2 emission and the comparative amount of CO2 emission. Accordingly, it is possible to determine the amount of CO2 emission produced by using the gas appliance and the difference between the amount of CO2 emission and the comparative amount of CO2 emission.