The present invention relates to a structure having a variable diameter, the structure including: a bolt which extends in a longitudinal direction a body which is disposed at one side of the bolt so as to surround the bolt a core which is disposed in the longitudinal direction of the bolt a plurality of extensions which is radially disposed outside the core and a plurality of outer shells which surrounds the extensions so as to correspond to the extensions, in which the extensions are expanded outward or contracted in a direction toward a center thereof by the core in accordance with a rotation direction of the bolt, such that a diameter of an outer circumferential surface of the extensions is changed.
