PROBLEM TO BE SOLVED: To provide a cap that enables generation of vaporized gas from a volatilization agent when needed such as immediately before use, facilitates charging of a volatilization agent, and has excellent handleability.SOLUTION: A cap comprises: a cylindrical cap body 3 with a top which is mounted to a mouth 21 of a container body 2 for accommodating a volatilization agent W and in which an insertion hole 31 opening into the container body 2 is formed and a lid body 4 which is mounted to the cap body 3, and opens and closes a communication hole 31. The communication hole 31 is formed in a top wall part 33 of the cap body 3. The lid body 4 includes a mounting cylindrical part 41 rotatably mounted to the cap body 3 around a cap axis O, and a cylindrical opening/closing lid 42 with a top mounted and connected to the mounting cylindrical part 41. A volatilization window 46 communicating with the insertion hole 31 is formed in a peripheral wall part 44 of the opening/closing lid 42. The cap body 3 is provided with a cap 1, in which an opening/closing plate 38 for opening and closing the volatilization window 46 along with the rotational movement of the lid body 4 around the cap shaft O to the cap body 3 projects.
