Gas sensor

A gas sensor comprising:

• a layered body that is formed by stacking a plurality of oxygen ion-conductive solid electrolyte layers, and that includes, formed therein, a measurement-object gas flowing portion in which a measurement object gas is introduced and flowed and a reference gas introducing space in which a reference gas used as a standard for detection of a specific gas concentration in the measurement-object gas is introduced,
• a reference electrode that is formed inside of the layered body, and that receives the reference gas introduced therein via the reference gas introducing space,
• a measurement electrode provided on an inner peripheral surface of the measurement-object gas flowing portion,
• a measurement-object gas side electrode provided in a region of the layered body that is exposed to the measurement-object gas,
• a detecting device that detects the specific gas concentration in the measurement-object gas based on an electromotive force generated between the reference electrode and the measurement electrode, and
• a reference gas adjusting device that pumps in oxygen to a periphery of the reference electrode by a flow of control current between the reference electrode and the measurement-object gas side electrode,
• wherein an average current density of the reference electrode under the flow of the control current is higher than 0 μA/mm2 and lower than 400 μA/mm2.