Abstract: Device for releasing a remaining gas which can easily puncture a hole without involving danger and a cap of a pressure can container which removably stores such a device. The remaining gas releasing device has a flexible sponge plate, a push pin member with its pin portion fitted into the center of one of the surfaces of the sponge plate, a center hole rigid sheet member positioned around the push pin member, a gas-impermeable rigid sheet plate bonded to the surfaces of the center hole rigid plate member, an adhesive sheet plate bonded to the other surface of the sponge plate so that the other surface is covered therewith and having a small hole at its center, and a release sheet plate peelably bonded to the adhesive sheet plate.