A gas sensor according to the present application includes a detecting device that detects a specific gas concentration of a measurement-object gas based on an electromotive force generated between a reference electrode and a measurement electrode; and a reference gas regulating device that flows an oxygen pumping current between the reference electrode and a measurement-object gas side electrode and pumps oxygen from around the measurement-object gas side electrode to around the reference electrode, wherein when the average value of the oxygen pumping current is P and the limiting current value of a reference gas introduction layer when oxygen is pumped from around the reference electrode to around the measurement-object gas side electrode is Q, the ratio Q/P is from 0.8 to 10.