PURPOSE: To prevent the corrosion of the inside circumferential part of a shell by applying underlying plating in the state of a shell in a shelled watch case of a wristwatch or the like.

CONSTITUTION: Underlying plating 1a of NiP, PDP, etc. is applied at several microns on a shell 1. This shell is mounted in an insert mold, and is insert molded by a high polymer material such as phenolic resin, "Ryton", polycarbonate or the like, whereby a case band 2 is formed. Next, the outside circumferential part of the shell 1 of the case band 2 is polished to finish the surface. At this time, the underlying plating 1a having been applied on the outside circumferential part is removed by the polishing. However, the underlying plating 1a existing between the shell 1 and the plastic body 2a remains. Gold plating is applied on the polished case band, whereby the finished product is obtained.