There is provided a control device for a gas sensor. The gas sensor is formed with first and second oxygen pumping cells to define first and second measurement chambers. Under the control of the sensor control device, the first and second oxygen pumping cells effect oxygen pumping actions against the first and second measurement chambers, respectively. The sensor control device is configured to detect currents through the first and second oxygen pumping cells, calculate a correction coefficient by comparison of a detection value of the first oxygen pumping cell current at a known oxygen concentration period with a previously stored reference value, correct the first oxygen pumping cell current by the correction coefficient and determine the concentration of nitrogen oxide in the gas under measurement based on the corrected first oxygen pumping cell current and the detected second oxygen pumping cell current.