PROBLEM TO BE SOLVED: To provide a generation stop method of chlorine dioxide gas capable of immediately stopping generation of chlorine dioxide gas.SOLUTION: Chemical reaction is stopped by introducing a reaction stop agent e including basic substance into a container 13, in a chlorine dioxide gas generating device 1 for supplying sodium chlorite and an acidic solution b to the container 13 and generating chlorine dioxide gas c by chemical reaction of them. The reaction stop agent e is stored in a reaction stop agent container 31 formed at a closed space, and when the chemical reaction is stopped, inside of the reaction stop agent container 31 may be released to room air, for introducing the reaction stop agent e into the container 13. After introduction of the reaction stop agent e into the container 13 for stopping the chemical reaction, thiosulfate or sulfite as a harmless agent may be introduced into the container 13 for achieving harmless. In addition, when chemical reaction is completed or stopped, the chlorine dioxide gas c may be passed to a catalyst filter 55 for being decomposed.
