An extendible structure includes at least three extendible longerons and a plurality of integrated radial spacers. Each spacer includes a plurality of legs integrally formed therewith to radially extend from the central part thereof. The distal end of each of the spacers is connected to a corresponding one of the extendible longerons. In the extended state of the extendible structure, at least three longerons are deployed in parallel with one another with space intervals among them in the lateral direction which intersect with the direction of extension of the longerons, and the spacers support the longerons with the horizontally spaced interval within a plane substantially perpendicular to the direction of extension of the longerons. In the collapsed condition of the extendible structure, each of the longerons is collapsed in a loop form, and the spacers are laid one upon another inside the loop formed by the longerons while the legs of the spacers are twisted.