PURPOSE: To inexpensively obtain a small sensor, by using at least one of a plurality of electrodes or leads of an oxygen sensor element in common to the single side of a thermocouple.

CONSTITUTION: One and other porous platinum electrodes 2, 4 formed to both end surfaces of the leading side of an ion conductive solid electrolyte 1 constitute the electrodes of an oxygen sensor. A porous electrode 3 comprising material quality such as a platinum-rhodium alloy forms a thermocouple 5 along with the platinum electrode 2. When voltage Vp is applied to an oxygen sensor element from a voltage source 13, a limit current Ip corresponding to the concn. of oxygen is outputted to a detector 14. The temp. of the leading side of an element appears on the detector 14 as output Vt by the electromotive force generated in a thermocouple part 5 being the connection part of the platinum electrode 2 and platinum-rhodium electrode 3 of the solid electrolyte 1. The voltage applied to the sensor element is corrected by said output Vt or the heater for heating the sensor is controlled by the output Vt to enable the correction of the temp. of sensor output Ip.