PURPOSE: To apply a ready and safe insecticidal treatment to an insecticidal object by constructing an air-tight tent, etc., for accommodating the insecticidal object, supplying a mixture gas containing a specified ratio of gaseous carbon dioxide and ozone gas thereto and utilizing its high insecticidal effect ad deodorizing effect.

CONSTITUTION: An air-tight tent 8, etc., is constructed for accommodating an insecticidal object such as a house 15. Carbon dioxide gas from a carbon dioxide gas cylinder 4 and ozone gas generated by an ozone gas generator 3 are mixed in a mixing box while detecting the concentrations of the respective gases by gas concentration sensors 11 and 12, controlling a valve 10 and an electromagnetic valve 13 by their electrical signals and keeping the mixture ratio of carbon dioxide gas to ozone gas within a range of 3:1 to 1:3. The resultant mixture gas is subsequently supplied to the tent 8, etc., and the waste mixture gas is then allowed to pass through an active carbon tank 16 and an edible salt water tank 17 in order and subsequently discharged into the outside air. This method enables application of a safe and ready insecticidal treatment to an insecticidal object by a high insecticidal effect and a high deodorizing effect.