a flow path for flow of a gas;

a flow rate measurement unit for measuring a flow rate of the gas flowing through the flow path;

a first absolute pressure sensor mounted inside the flow path and configured to measure an absolute pressure of the gas;

a second absolute pressure sensor mounted outside the flow path and configured to measure an absolute pressure of an atmospheric pressure;

a gas pressure determination unit configured to measure a change in a gas supply pressure from the absolute pressure of the gas and the absolute pressure of the atmospheric pressure measured by the first absolute pressure sensor and the second absolute pressure sensor, respectively;

a shutoff valve configured to shut off the flow path; and

a control circuit configured to: (i) control the flow rate measurement unit; and (ii) cause the shutoff valve to shut off the flow path when determining an abnormality from the flow rate of the gas measured by the flow rate measurement unit or the change in the gas supply pressure measured by the gas pressure determination unit,

wherein:

the flow rate measurement unit is mounted inside the flow path, the flow rate measurement unit including a measurement circuit;

the first absolute pressure sensor is mounted on the measurement circuit;

the control circuit is mounted outside the flow path; and

the second absolute pressure sensor is mounted on the control circuit.