PURPOSE: To prevent corrosion despite infiltration of a plating soln. into the inside circumferential part of a shell in the stage of finish plating by providing a coating film of high polymer paint in the state of a shell in a shelled watch case such as wristwatch case of the like.

CONSTITUTION: Coating film 1a of high polymer type paint of acrylic type, epoxy type, "Teflon" type, etc. is applied over the entire surface of the inside circumferential part of a sheel 1 or the surface of the shell. This shell is mounted to an insert mold for plastic molding material, and a high polymer material is molded on the inner side of the shell 1 by insert molding, whereby a plastic body part 2a is made. Next, this is polished to have better appearance. At this time, the coating film applied on the outside circumferential part is removed by the polishing. However, the coating film 1a existing between the shell 1 and the plastic body 2a remains. After underlying plating is applied, an Au type plating layer 2a is formed only on the outside circumferential surface of the shell 1.