Oxygen concentration detecting device

An oxygen concentration detecting device includes at least one oxygen concentration detecting element formed by an oxygen-pumping element and a cell element, composed of an oxygen ion-conductive wall, separating a pair of electrodes. The oxygen-pumping element and cell element define a gas diffusion chamber. A current detecting resistance forms a series circuit with the oxygen-pumping element. A voltage applying circuit applies to the series circuit an output voltage corresponding to the difference between a voltage between the electrodes of the cell element and a first reference voltage. An output detecting circuit outputs a voltage signal corresponding to a value of pumping current flowing through the resistance. An operational amplifier has a non-inverting input terminal supplied with a second reference voltage, an inverting input terminal connected to one end of the resistance, and an output terminal connected to the other end of the resistance. The output detecting circuit detects a first voltage at the one end of the resistance and a second voltage at the other end and outputs the voltage signal corresponding to the difference between the detected first and second voltages. The output detecting circuit corrects the voltage signal based upon the first and second voltages which are obtained in a state where no pumping current is supplied to the resistance. Electrodes of the oxygen-pumping element and the cell element are connected together within the gas diffusion chamber or within the basic body of the sensor body.