Abstract: A substantially annular-shaped accessory includes multiple arc-shaped structural elements that form a C-shaped annulus (major arc-shaped annulus) and a core. The core has a structure formed into a C-shaped annular-shaped accessory having an end gap of expandable/contractible width. One end of the core having a C-shaped member and an elastic body are fasten to a locking projection inside the arc-shaped structural element constituting one end section. Another end of the core is fasten to the locking projection inside the arc-shaped structural element constituting another end section.