A chlorine dioxide generator includes a container body deformable in response to application of a force from the outside. The container body contains therein a solid acidic composition and an aqueous chlorite solution under a non-contact state from each other. The solid acidic composition comprises a porous material containing an acidic substance. The aqueous chlorite solution is sealed within an easily breakable enclosure. In operation, when the container body is deformed, the enclosure contained therein is broken to bring the aqueous chlorite solution into contact with the solid acidic composition, whereby chlorine dioxide gas is generated. This generated chlorine dioxide gas is discharged via a gas discharge port to the outside of the container body.