To provide a self-diagnostic device of gas meter capable of diagnosing whether the integration of a gas meter is normal or not by the meter itself and performing an alarm processing in the determination of abnormality.

This device is formed of a flow measuring means 21 for measuring a gas flow rate, a flow rate change determining means 23-1 for determining the flow rate change, a pressure measuring means 22 arranged in the meter inlet part 19 of a gas meter to measure the gas pressure at the meter inlet, a control means 23 for starting the pressure measuring means 22 on the basis of the determination result of the flow rate change determining means 23-1, a pressure memory means 24 for storing the measured pressure in the presence of flow from the pressure measuring means 22, a proper pressure determining means 23-2 for comparing the measured pressure in the absence of flow from the pressure measuring means 22 with the stored pressure from the pressure memory means 24 to determine whether the measured pressure is lower than the stored pressure or not, and an alarm means 25 for performing an alarm processing when the measured pressure in the absence of flow is determined lower than the stored pressure.