A gas meter comprising: a flow rate detector configured to detect a flow rate value of gas; a shutoff valve configured to shut off the gas; a pressure detector configured to detect a pressure value of the gas; and a leak detector configured to - detect a first flow rate value, a first pressure value and a first average flow rate value Q1 and a first average pressure value P1, which are average values of first flow rate values and first pressure values, respectively, after a predetermined time has elapsed since opening of the shutoff valve, - detect a second flow rate value, a second pressure value and a second average flow rate value Q2 and a second average pressure value P2, which are average values of second flow rate values and second pressure values, respectively, after a predetermined time has elapsed since closing of the shutoff valve, - calculate a flow rate difference value ΔQ = Q2 - Q1 and a pressure difference value ΔP = P2 - P1, and - determine a gas leak if the flow rate difference value ΔQ is less than a leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a first pressure drop determination value Pa or if the flow rate difference value ΔQ is more than or equal to the leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a second pressure drop determination value Pb, characterized in that the gas meter further comprises a display and is configured to - convert the flow rate difference value ΔQ into a code by a code conversion table, - convert the pressure difference value ΔP into a code by a code conversion table, - create a two-digit composite code with the obtained code of the flow rate difference value ΔQ as an upper digit and the pressure difference value ΔP as a lower digit, and - display the composite code on the display. a flow rate detector configured to detect a flow rate value of gas; a shutoff valve configured to shut off the gas; a pressure detector configured to detect a pressure value of the gas; and a leak detector configured to - detect a first flow rate value, a first pressure value and a first average flow rate value Q1 and a first average pressure value P1, which are average values of first flow rate values and first pressure values, respectively, after a predetermined time has elapsed since opening of the shutoff valve, - detect a second flow rate value, a second pressure value and a second average flow rate value Q2 and a second average pressure value P2, which are average values of second flow rate values and second pressure values, respectively, after a predetermined time has elapsed since closing of the shutoff valve, - calculate a flow rate difference value ΔQ = Q2 - Q1 and a pressure difference value ΔP = P2 - P1, and - determine a gas leak if the flow rate difference value ΔQ is less than a leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a first pressure drop determination value Pa or if the flow rate difference value ΔQ is more than or equal to the leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a second pressure drop determination value Pb, characterized in that - detect a first flow rate value, a first pressure value and a first average flow rate value Q1 and a first average pressure value P1, which are average values of first flow rate values and first pressure values, respectively, after a predetermined time has elapsed since opening of the shutoff valve, - detect a second flow rate value, a second pressure value and a second average flow rate value Q2 and a second average pressure value P2, which are average values of second flow rate values and second pressure values, respectively, after a predetermined time has elapsed since closing of the shutoff valve, - calculate a flow rate difference value ΔQ = Q2 - Q1 and a pressure difference value ΔP = P2 - P1, and - determine a gas leak if the flow rate difference value ΔQ is less than a leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a first pressure drop determination value Pa or if the flow rate difference value ΔQ is more than or equal to the leak determination flow rate Qa and the pressure difference value ΔP is more than or equal to a second pressure drop determination value Pb, characterized in that the gas meter further comprises a display and is configured to - convert the flow rate difference value ΔQ into a code by a code conversion table, - convert the pressure difference value ΔP into a code by a code conversion table, - create a two-digit composite code with the obtained code of the flow rate difference value ΔQ as an upper digit and the pressure difference value ΔP as a lower digit, and - display the composite code on the display. - convert the flow rate difference value ΔQ into a code by a code conversion table, - convert the pressure difference value ΔP into a code by a code conversion table, - create a two-digit composite code with the obtained code of the flow rate difference value ΔQ as an upper digit and the pressure difference value ΔP as a lower digit, and - display the composite code on the display.