Gas sensor

A gas sensor for detecting a target gas to be measured in a measurement-object gas, the gas sensor comprising a sensor element and a control unit for controlling the sensor element, wherein

• the sensor element comprises:
• a base part in an elongated plate shape, including an oxygen-ion-conductive solid electrolyte layer;
• a measurement-object gas flow cavity for introduction and flow of a measurement-object gas, formed from one end part in a longitudinal direction of the base part;
• a reference gas chamber formed inside the base part, and being separated from the measurement-object gas flow cavity and closed inside the base part;
• a reference electrode disposed in the reference gas chamber;
• and
• a pump electrode disposed at a position different from the reference gas chamber, and
• the control unit comprises:
• a storing part storing in advance, a required amount of oxygen to be present in the reference gas chamber at a time at which oxygen concentration in a reference gas in the reference gas chamber is a predetermined concentration;
• and
• a processing part performing refresh processing in which a current is applied between the pump electrode and the reference electrode to pump out oxygen present in the reference gas chamber from the reference gas chamber, and then pump oxygen into the reference gas chamber in the required amount of the oxygen which is stored in advance by the storing part.