The present invention relates to a container cap with an additive-containment structure which classifies component materials to preserve the component materials in one container and is used to artificially mix the component materials to manufacture a liquid such as a soft drink made of a plurality of materials. More specifically, a container cap with an additive-containment structure comprises a cylindrical additive-containment room which is integrated with the upper surface of a cap body, and has a closed upper part; a button unit which is installed inside the additive-containment room and is curved upwards to selectively open the additive-containment room; a containment room opening means including a cutout rod protruding downwards from the center of the bottom part of the button unit; and a support protrusion which is located on the entrance of the container and the inner surface of the cap body, and holds and supports the lower end of the cutout rod not to be slipped from the center of a packing forming the floor part of the additive-containment room to guide smooth cutout. The container cap is simply formed by reducing the number of components, thereby reducing manufacturing processes and production costs; and has a one-touch bottom type structure enabling the additive-containment room to be opened, thereby improving convenience in use.COPYRIGHT KIPO 2015