[Problem] To provide a pathogenic microbe and insect pest extermination method and a pathogenic microbe and insect pest extermination device, which are capable of efficiently generating OH radicals and have excellent pathogenic microbe- and insect pest-exterminating effects. [Solution] Pathogenic microbes or insect pests are exterminated by: introducing water as a water mist, etc. into a reaction vessel (2); supplying a gas for forming a plasma from a gas supply unit (3) to the reaction vessel (2); applying a voltage between a cathode (5) and an anode (6) disposed in the reaction vessel (2) and electrically discharging the gas and generating OH radicals; and irradiating the OH radicals on the objects in which microbes or insects are to be killed. The gas is air, helium or argon, or a mixture of said gases. The amount of OH radicals generated can be controlled by controlling the volume of water mist supplied or the volume of gas supplied.
