Gas sensor

A gas sensor comprising:

• a sensor element including
• an element body which includes an oxygen-ion-conductive solid electrolyte layer, and is internally provided with a measurement-object gas flow portion that introduces a measurement-object gas and flows the measurement-object gas,
• a measurement pump cell having an outer measurement electrode provided outside the element body to be in contact with the measurement-object gas, and an inner measurement electrode disposed in a measurement chamber of the measurement-object gas flow portion, the measurement pump cell being configured to pump out oxygen from surroundings of the inner measurement electrode to surroundings of the outer measurement electrode,
• a reference electrode disposed inside the element body to come into contact with a reference gas which serves as a reference for detection of a specific gas concentration in the measurement-object gas, and
• a measurement voltage detection sensor cell that detects a measurement voltage between the reference electrode and the inner measurement electrode;
• a pump cell controller that executes a normal time measurement pump control process of pumping out oxygen in the measurement chamber during a normal operation time of the sensor element by controlling the measurement pump cell so that the measurement voltage reaches a normal time target value, and executes a start-up time measurement pump control process of pumping out oxygen in the measurement chamber at a start-up time of the sensor element earlier than the normal operation time by controlling the measurement pump cell so that the measurement voltage reaches a start-up time target value higher than the normal time target value;
• and
• a specific gas concentration detection section that detects the specific gas concentration in the measurement-object gas based on a measurement pump current which flows through the measurement pump cell by the normal time measurement pump control process.