To provide a form for forming a specimen wherein both cylindrical components can be prevented from being shifted radially and axially by a simple structure, and assembly and decomposing operation are easy.

A cylindrical component 19 is constituted by making both contact parts of a pair of cylindrical components 10 wherein a sectional shape is arcuate and contact parts 13 and 14 are formed on both edges contact against each other. A lower part holding component 22 wherein a lower part fitting part 22a fitting to a periphery of a lower end part of the cylindrical component 19 and a lower end contact part 22b contacting to the lower end of the cylindrical component 19 are formed, and a cylindrical upper part holding component 23 wherein an upper fitting part 23a fitting to the periphery of the upper end part of the cylindrical component 19 and a cylindrical upper end contact part 23b contacting to the upper end of the cylindrical component 19 are formed, are provided.