A supporting apparatus such as a portable seat that can be opened and closed is disclosed having a plurality of poles hinged to junctions. A part of the poles form the legs and another portion form an anchorage on which a foldable surface is stretched when the apparatus is opened. The apparatus also includes traction elements cooperating with the folding surface and which join one another at the end of the poles that do not converge at the junctions. The configuration preset by the orientation of the poles, along with the structural configuration of anti-prism or other extremely stable and rigid configurations, are such that they spread most of the torsional and bending stresses.