To provide a cap body used in a mixing container cap housing powder to be mixed with a container content, wherein the cap body is capable of effectively preventing the mixing powder, which is housed in the container cap, from absorbing moisture.

The plastic cap body includes a top plate part 40, and a skirt-like lateral wall 41 extending downward from the periphery of the top plate part 40. A cutter 50 for rupturing sealing foil extends downward from the inner surface of the top plate part 40. The cutter 50 for rupturing the sealing foil is formed of a moisture-absorbing thermoplastic resin composition in which a drying agent is dispersed.