A gas meter device is provided which is configured in a manner that even if a user takes an unauthorized action such as the removal of a gas meter device in order to use gas without authorization, since the generation of a particular flow-rate change profile different from a normal flow-rate change profile of a gas appliance is detected, the sign of the tamper of the gas can be detected, whereby the tamper of the gas can be prevented. The gas meter device includes an appliance determining unit 6 for determining a gas appliance being used and a tamper determining unit 7 which determines that the gas is used without authorization in the case where the particular flow-rate change profile different from an appliance determining value registered in a registration storage unit 5 is generated.