A cap is removably fitted over a mouth of a container and includes a molded plastic product formed of plastic and a molded paper product formed mainly of a paper biomass material and joined to the molded plastic product. The material of the molded paper product accounts for more than 50% by mass of the total materials for the cap. The molded plastic product includes a lid for opening and closing the mouth and a joining section for joining to the molded paper product. The molded paper product includes a receiving section joined to the joining section and a cylindrical portion extending from the receiving section.