Controller for gas concentration sensor

A controller comprises an impedance detection unit for applying an impedance detection voltage to the sensor and detect device impedance; and reverse voltage application unit for applying the same voltage as generated by the sensor itself or a voltage that shifts same voltage against a direction of impedance detection voltage for specified period of time. The controller also has data invalidation unit for invalidating the output of the sensor for a specified period of time after detection voltage is applied; and an impedance detection time interval setup unit for increasing specified time intervals with an increase in device impedance.