An appliance monitoring apparatus comprising: a flow detection unit to be disposed in a gas flow path in a gas meter and configured to detect a gas flow; an appliance determination unit configured to determine a gas appliance used by a client by leaning a flow value used by the client and a gas consumption time in accordance with a signal from the flow detection unit, and to output a gas flow signal used by the gas appliance; characterized by: a CO 2 emission data storage unit configured to store an amount of a CO 2 emission previously determined for each type of the gas appliance as database; and a CO 2 emission calculation unit configured to compute, integrate, and store an amount of CO 2 emission based on the CO 2 emission data pertaining to a gas appliance selected from the CO 2 emission data storage unit on receipt of a signal from the appliance determination unit, a gas flow of the selected gas appliance, and a gas consumption time of the selected gas appliance, wherein every time the integrated and stored amount of CO 2 emission has exceeded a plurality of values of preset amounts of CO 2 emissions, the CO 2 emission calculation unit outputs an indication that the integrated and stored amount of CO 2 emission has exceeded any of the plurality of values of preset amounts of CO 2 emissions to an outside. a flow detection unit to be disposed in a gas flow path in a gas meter and configured to detect a gas flow; an appliance determination unit configured to determine a gas appliance used by a client by leaning a flow value used by the client and a gas consumption time in accordance with a signal from the flow detection unit, and to output a gas flow signal used by the gas appliance; characterized by: a CO 2 emission data storage unit configured to store an amount of a CO 2 emission previously determined for each type of the gas appliance as database; and a CO 2 emission calculation unit configured to compute, integrate, and store an amount of CO 2 emission based on the CO 2 emission data pertaining to a gas appliance selected from the CO 2 emission data storage unit on receipt of a signal from the appliance determination unit, a gas flow of the selected gas appliance, and a gas consumption time of the selected gas appliance, wherein every time the integrated and stored amount of CO 2 emission has exceeded a plurality of values of preset amounts of CO 2 emissions, the CO 2 emission calculation unit outputs an indication that the integrated and stored amount of CO 2 emission has exceeded any of the plurality of values of preset amounts of CO 2 emissions to an outside. a CO 2 emission data storage unit configured to store an amount of a CO 2 emission previously determined for each type of the gas appliance as database; and a CO 2 emission calculation unit configured to compute, integrate, and store an amount of CO 2 emission based on the CO 2 emission data pertaining to a gas appliance selected from the CO 2 emission data storage unit on receipt of a signal from the appliance determination unit, a gas flow of the selected gas appliance, and a gas consumption time of the selected gas appliance, wherein every time the integrated and stored amount of CO 2 emission has exceeded a plurality of values of preset amounts of CO 2 emissions, the CO 2 emission calculation unit outputs an indication that the integrated and stored amount of CO 2 emission has exceeded any of the plurality of values of preset amounts of CO 2 emissions to an outside.