Provided are a method and a device for sterilizing the surface of a space-to-be-sterilized which are safe to the human body, which are effective even for sterilizing spore-forming bacteria, which do not require the space-to-be-sterilized to be highly shielded, and which can sterilize the surface of the space efficiently with inexpensive equipment. The disclosed method involves: spraying a low-concentration sterilizing agent in the form of fine particles into the space-to-be-sterilized and making the sterilizing agent adhere to the surface thereof, the low-concentration sterilizing agent being any one of a 1-10 wt % aqueous solution of hydrogen peroxide, a 0.1-1 wt % aqueous solution of peracetic acid, or a 0.01-0.1 wt % aqueous solution of hypochlorous acid; adjusting the humidity in the space-to-be-sterilized; and air-drying the sterilizing agent. Thus, a high level of sterilization can be achieved in a short time and at low cost.