To provide a link structure that is used for toys and the like and reversibly expandable.

This reversibly expandable structure 500 includes loop assembly 510 containing a pair of interactive coupling of polygonal links. Each loop assembly 510 has a polygonal link equipped with at least 3 journalling joints. The polygonal link lies on a surface plane of the structure or on a plane parallel to the surface. The polygonal link has a center journalling joint to form pairs of links 520, 530, 540, 550, 560 coupling with other polygon links. The polygonal link also has at least one internal journalling joint and one peripheral journalling joint. The internal journalling joint is used to form a loop assembly connecting a pair of links to a neighboring pair of links. The loop assembly can form a structure being coupled to other loop assembly or other pair of links through the peripheral journalling joint.