Abstract
This paper describes decontamination of the environmental surface of an unmanned room by chlorine dioxide gas. Chlorine dioxide gas is harmful to the human body, so for safety, it is necessary to be careful not to leak it from the target room. In addition, since chlorine dioxide is corrosive, it is also necessary to consider protecting or evacuating indoor articles. Because there is a trade-off between the decontamination effect of chlorine dioxide and the damage caused by corrosion, it is necessary to determine the decontamination conditions （gas concentration, humidity, treatment time） in consideration of both. Furthermore, in order to obtain a sufficient decontamination effect, it is necessary to devise a method to make the entire room uniform at a predetermined gas concentration.
