PROBLEM TO BE SOLVED: To provide an insecticidal method of pests, capable of killing pests which adhere to the surfaces of not only relatively hard farm crops but also growing plants or relatively soft farm crops, and pests which sneak into the inside.SOLUTION: An insecticidal method of pests includes: a decompression step of decompressing a pressure inside a warehouse where plants, farm crops or cereals are stored a carbon dioxide injection step of injecting carbon dioxide into the inside of the warehouse after the decompression step and a pressure recovery step of recovering a pressure inside the warehouse to an original pressure after the carbon dioxide injection step, and bringing a concentration of carbon dioxide in the warehouse to 40 vol.% to 60 vol.%. The decompression step, the carbon dioxide injection step, and the pressure recovery step are executed one time or repeated a plurality of times.
