To provide a cap structure which embodies a means that permits release of gas without any leakage of contents (in particular, liquid) that spontaneously emits gas (gaseous body) within a container, by mounting a packing into a cap by subjecting the packing to a simple work.

The cap intended for degassing provides two types of means of releasing gas emitted spontaneously within the container, one type using, in a popular cap, a popular packing and a packing with a space made by working a packing material, and the other type using a combination of a cap worked as to provide a space therein and a popular packing, both means making for the same mechanism and effect for suspending the packing by inner pressure.