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, 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 when determining based on an operation of the measurement pump cell that an oxygen concentration in the measurement chamber is stabilized, makes switching from the start-up time measurement pump control process to the normal time measurement pump control process;
• 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.