to 8 whereas that of the spring materials made from phosphore bronze etc is lower than 1 in the invention simple attachment of parts and high reliability are satisfied by simultaneously utilizing both said shape memory effect and superelasticity effect as the shape memory alloys with superelasticity usable for the materials of the reinforcing fastener of the invention ni ti type alloy alloy mainly composed of intermetallic compounds between ni and ti or alloys substituting a part of either or both of ni and ti with other elements such as fe co cu cr etc and cu zn type cu al type cu zn al type fe si mn type fe ni cr type fe nico ti type and other type alloys can be mentioned thereamong the use of ni ti type alloy is particularly preferable the af point of the alloy can be established advantageously between 0 u00b0 and 20 u00b0 c in order to recover to the memorized shape in the vicinity of normal temperature as the shapes of the fastener any of horseshoe shape circular shape elliptic shape and flattened elliptic shape in section shown in fig2 a through d may be used but the horseshoe shape in section in a is preferable if the section is circular shape the bulge when attached to the connection part is large resulting in the connector not only becoming too thick compared.