A facility apparatus comprising: - a circulation path through which a solvent circulates; - a corrosion protection performance degradation detection sensor that is adapted to detect a change in concentration of a corrosion inhibitor contained in the solvent, the corrosion protection performance degradation detection sensor comprising: - a detection electrode that is adapted to react with the corrosion inhibitor contained in the solvent and that is able to have an electrode surface film on a surface thereof, the electrode surface film inhibiting corrosion; - a counter electrode that is disposed so as to face the detection electrode with a predetermined distance therebetween; and - an AC power supply that is adapted to apply an AC voltage level with a predetermined frequency and a predetermined voltage between the detection electrode and the counter electrode; the facility apparatus characterized by comprising: - a liquid feeding pump that is adapted to supply the corrosion inhibitor to the circulation path, the corrosion inhibitor inhibiting corrosion of an anticorrosion target material forming the circulation path; and a controller that is adapted to control an operation of the liquid feeding pump, on a basis of a change in impedance of the electrode surface film formed on the detection electrode at a time when the AC voltage with the frequency of less than 1 kHz and more than 1 Hz is applied between the detection electrode and the counter electrode, - wherein the corrosion protection performance degradation sensor is adapted to detect the change in impedance of the electrode surface film, so as to detect a change in the concentration of the corrosion inhibitor in the solvent before pitting occurs, and so as to detect a change in the electrode surface film from a corrosion inhibition period to a pitting inhibition period, and - wherein the controller is configured to obtain, in advance, an impedance at a time when the electrode surface film of the detection electrode is in a pitting initiation state, as a lower limit, and configured to start the liquid feeding pump when the impedance of the electrode surface film formed on the detection electrode falls below the lower limit. - a circulation path through which a solvent circulates; - a corrosion protection performance degradation detection sensor that is adapted to detect a change in concentration of a corrosion inhibitor contained in the solvent, the corrosion protection performance degradation detection sensor comprising: - a detection electrode that is adapted to react with the corrosion inhibitor contained in the solvent and that is able to have an electrode surface film on a surface thereof, the electrode surface film inhibiting corrosion; - a counter electrode that is disposed so as to face the detection electrode with a predetermined distance therebetween; and - an AC power supply that is adapted to apply an AC voltage level with a predetermined frequency and a predetermined voltage between the detection electrode and the counter electrode; - a liquid feeding pump that is adapted to supply the corrosion inhibitor to the circulation path, the corrosion inhibitor inhibiting corrosion of an anticorrosion target material forming the circulation path; and a controller that is adapted to control an operation of the liquid feeding pump, on a basis of a change in impedance of the electrode surface film formed on the detection electrode at a time when the AC voltage with the frequency of less than 1 kHz and more than 1 Hz is applied between the detection electrode and the counter electrode, - wherein the corrosion protection performance degradation sensor is adapted to detect the change in impedance of the electrode surface film, so as to detect a change in the concentration of the corrosion inhibitor in the solvent before pitting occurs, and so as to detect a change in the electrode surface film from a corrosion inhibition period to a pitting inhibition period, and - wherein the controller is configured to obtain, in advance, an impedance at a time when the electrode surface film of the detection electrode is in a pitting initiation state, as a lower limit, and configured to start the liquid feeding pump when the impedance of the electrode surface film formed on the detection electrode falls below the lower limit.