To use a general-use piston-cylinder unit to a constituent element tensing device by relatively, adjustably providing both a first retaining element connected to a piston rod by means of a guide element guided by the external surface of the cylinder, and a second retaining element immovably held to the cylinder.

A guide element 25 is connected to the end part of the piston rod 18 of a piston-cylinder unit 8. The guide element 25 is provided with a first retaining element 28 consisting of a retaining surface 29 extending inside the plane in which a set axis 12 is positioned at right angles, and also the retaining surface 29 is disposed so as to be eccentric to the set axis 12. A retaining plane 11 is farmed so as to form a part of two finger parts of a retaining element 10, and is arranged so as to be laterally and partially superimposed to the retaining surface 29 of the first retaining element 28. The guide element 25 is arranged to surround a cylinder 15, and is guided by the cylinder 15. The second retaining element 10 is supported on a flange 4 so as to be immovable to the cylinder 25.