A chlorine dioxide generator configured to generate chlorine dioxide gas through a reaction between a chlorite and an acidic substance, the chlorine dioxide generator comprising: a container body which is deformable in response to application of a force thereto from the outside; wherein the container body includes a gas discharge port formed of a gas-permeable, water-impermeable or gas-permeable, water-permeation retardant member, the container body except for the gas discharge port being sealed, thus having a water-impermeable construction; the container body contains therein a solid acidic composition and an aqueous chlorite solution under a non-contact condition from each other; the solid acidic composition comprises a porous material containing an acidic substance that exhibits acidity when dissolved in water; the aqueous chlorite solution is sealed within an easily breakable enclosure; wherein the chlorine dioxide generator is configured so that, 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 and this chlorine dioxide gas is discharged via the gas discharge port to the outside of the container body, characterized in that the porous material is disposed closer to the gas discharge port than to the enclosure, and that the chlorine dioxide generator further comprises an insulating member for insulating the porous material and the enclosure from each other, the insulating member having at least one hole portion and being disposed in such a manner as to be capable of preventing displacement of the porous material toward the enclosure. a container body which is deformable in response to application of a force thereto from the outside; wherein the container body includes a gas discharge port formed of a gas-permeable, water-impermeable or gas-permeable, water-permeation retardant member, the container body except for the gas discharge port being sealed, thus having a water-impermeable construction; the container body contains therein a solid acidic composition and an aqueous chlorite solution under a non-contact condition from each other; the solid acidic composition comprises a porous material containing an acidic substance that exhibits acidity when dissolved in water; the aqueous chlorite solution is sealed within an easily breakable enclosure; wherein the chlorine dioxide generator is configured so that, 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 and this chlorine dioxide gas is discharged via the gas discharge port to the outside of the container body, characterized in that the porous material is disposed closer to the gas discharge port than to the enclosure, and that the chlorine dioxide generator further comprises an insulating member for insulating the porous material and the enclosure from each other, the insulating member having at least one hole portion and being disposed in such a manner as to be capable of preventing displacement of the porous material toward the enclosure.