Conventionally, there has been known a sensor for detecting the concentration of nitrogen oxides (hereinafter, simply referred to as “NOX”), which is a specific type of gas contained in exhaust gas of an internal combustion engine. A proposed sensor control device which is connected to such a sensor is configured to amplify the output of the sensor by two amplification circuits operating in a wide range and a narrow range, respectively; selects one of the two amplified signals; and obtain the NOX concentration on the basis of the selected signal (see Patent Document 1). This proposed sensor control device can improve the detection accuracy of NOX concentration.