Fuente: Wipo "Sensorization" An SOx index acquisition apparatus for an internal combustion engine includes a sensor cell, a voltage source. The sensor cell includes a solid electrolyte and a pair of electrodes disposed so as to sandwich the solid electrolyte. The voltage source applies a voltage to the sensor cell. The apparatus acquires a resistance value of the sensor cell as a sensor resistance, decreases an applied voltage, which is a voltage that is applied to the sensor cell, from a predetermined voltage, acquires a current that passes through the sensor cell while the applied voltage is being decreased from the predetermined voltage, as an SOx sensor current, acquires a base SOx concentration, which correlates with an SOx concentration in exhaust gas, based on parameters including the SOx sensor current, and acquires the SOx concentration as an SOx index by correcting the base SOx concentration based on the sensor resistance.