A gas concentration detection apparatus is provided with a measuring gas chamber, a solid electrolyte body, a pump cell, a sensor cell, a pump cell controller and a sensor cell detection section. The pump cell controller applies an elimination voltage to the pump cell at a start-up point, before a gas concentration is detected. The water in the measuring gas chamber is decomposed and hydrogen is generated by application of the elimination voltage. Oxygen occluded in a sensor electrode of the sensor cell is removed by the hydrogen.