Nitrogen oxide is used to safely sterilize inside of a space area or an object arranged within the space area. A sterilization method is provided to comprise: introducing nitrogen oxide liquid stored in a vessel (4) into a space area (2, 2′, 2″) to gasify nitrogen oxide liquid, and sterilizing inside of space area (2, 2′, 2″) or object (1) arranged in space area (2, 2′, 2″) with nitrogen oxide gas evaporated from nitrogen oxide liquid to completely annihilate and destroy microorganisms inclusive of bacteria and virus with nitrogen oxide gas for preventing the infection by microorganisms to human body and damage to precision components.
