Gas sensor

The invention provides a gas sensor which simultaneously performs processing by using a first pump unit and processing by using a second pump unit with good precision. A gas sensor (100) is provided with a sensor element (101), first and second impedance measurement units (47a, 47b), and a control device. The sensor element includes: an element main body; a main pump unit (21) having an inner pump electrode (22); a measurement pump unit (41) having a measurement electrode (44); and a heater (72). A first impedance measurement unit (47a) measures a first impedance (R1) by applying a voltage to the inner pump electrode. A second impedance measurement unit (47b) measures a second impedance (R2) by applying a voltage to the measurement electrode. The control device controls the heater such that the first impedance reaches a target value (R1 *). On the basis of the second impedance, the control device corrects the pump current (Ip2) of the measurement pump cell, or corrects a value derived on the basis of the pump