PROBLEM TO BE SOLVED: To provide an indoor decontamination system capable of improving the decontamination capability firstly by reducing the space and cost by reducing the quantity of dust to the minimum necessary quantity, and secondary by exhibiting a desired decontamination capability with loading of a small quantity of hydrogen peroxide.SOLUTION: The indoor decontamination system B is for decontaminating a contamination target room 1 by using hydrogen peroxide. The indoor decontamination system B includes a release line for circulating air including hydrogen peroxide gas released from a hydrogen peroxide generating device 11 between the contamination target room 1 and the hydrogen peroxide generating device 11, and a degrading line for circulating air between the contamination target room 1 and a hydrogen peroxide degrading device 12 to sequentially degrade hydrogen peroxide included in air by the hydrogen peroxide degrading device 12. These lines are composed by using the same circulation ducts 6, 8 and 15.
