Gas meter and center device are provided. Gas meter includes flow rate measurer that measures a flow rate of gas in time series. Center device receives and analyzes flow rate data from gas meter, and monitors states of use of gas appliances. Gas meter detects the start of operation of gas appliances, and transmits flow rate data during predetermined periods before and after the start of operation in accordance with a request from center device. Center device monitors the states of use of gas appliances based on the received flow rate data.