PURPOSE: To form easily and continuously a beautiful uneven pattern having no crush nor dilation of a dressed surface by providing a guid part, a rib forming roll, an embossing roll and a forming roll group in the carrying direction of a thin plate material.

CONSTITUTION: A thin metallic plate A is fed onto a placing plate 2 of a guide part 1, and made to go straight on horizontally between a guide plate 3 and a giude roll 4. Subsequently, it is fed to a rib forming roll 5 and a rib is provided in parallel on a side edge position of a part which becomes a dressed surface. The plate is fed to an embossing roll 8 by using this rib as a guide, and an uneven pattern is embossed in the rib. Subsequently, the thin plate material A is fed to a recessed shape forming roll group 11 and formed to a recessed shape, and also a male and female die connecting part is formed on both lower end edges, and a desired hoop material is obtained. A cushion material of resistance to wear such as a synthetic resin, etc. is coated or provided vertically on the surface of a part corresponding to a pass line of this roll group 11.