To suppress an increase in nitrogen oxide while simultaneously keeping exhausted carbon monoxide concentration lower even when incineration pace is changed.

An incinerator is adapted such that oxygen-in-waste gas detection means 7 is provided in a flue 5 extending from a secondary combustion region of an incinerator 1 for incinerating refuse for detecting oxygen-in waste gas concentration to control the amount of secondary air such that the detected oxygen-in waste gas concentration is coincident with previously set object oxygen concentration. In the incinerator, there is provided object incineration pace set means 11 for setting the amount of incineration of thrown refuse per unit time to two or more stages. There is further provided object oxygen concentration set means 13 for setting object oxygen concentration as an index to adjust the amount of secondary air with respect to oxygen-in waste gas concentration detected by the oxygen-in waste gas detection means 7. The object oxygen concentration set means 13 is set to be higher than the object oxygen concentration set with respect to the object incineration pace higher than a predetermined amount when the object incineration pace is lower than a predetermined amount.