Gas sensor

A gas sensor comprising:

• a layered body that has a plurality of stacked layers of an oxygen-ion-conductive solid electrolyte and in which a measurement-object gas flowing portion that allows a measurement-object gas containing a specific gas to be introduced thereinto and to flow therethrough is provided;
• a measurement electrode that is disposed in at least a part of an internal surrounding surface of a measurement chamber formed in the layered body and communicating with the measurement-object gas flowing portion;
• a controller configured to:
• detect a concentration of the specific gas on the basis of a measurement pump current that flows when oxygen is pumped out from the atmosphere around the measurement electrode in the measurement chamber so that an oxygen concentration in the measurement chamber becomes a predetermined low concentration, the oxygen that is pumped out being oxygen that is generated when the specific gas is reduced in the measurement chamber or being oxygen that is generated when a gas obtained as a result of conversion of the specific gas to an oxide is reduced in the measurement chamber where the specific gas is a non-oxide;
• detect an air-fuel ratio of an atmosphere of the measurement-object gas on the basis of a regulating pump current;
• and
• correct the measurement pump current on the basis of an oxygen concentration of the measurement-object gas in accordance with the detected air-fuel ratio upon determining that the measurement-object gas is in a rich atmosphere based on the detected air-fuel ratio being equal to or smaller than a stoichiometric air-fuel ratio,
• determine a corrected value of the concentration of the specific gas contained in an exhaust gas of an internal combustion engine as the measurement-object gas on the basis of the corrected measurement pump current, and
• output the corrected value as the sensor output.