PURPOSE: To improve durability of installation devices for installing a fluid operation device between separated support elements by composing the installation devices of outward extending shoulders and a plurality of flexible fingers which end at tips having tapered coming surfaces.

CONSTITUTION: An air spring 14 is arranged between a bracket 40 of an upper structural element 12 and a circular housing 47 of a lower structural element 13, and fixed by means of an end cap installation device 15 and a piston installation device 16 from upper and lower sides. The cap installation device 15 is composed of an outer wall 52 formed with flexible fingers 58 arranged with same distances from a stem 60 having outwardly extending coming surface 64 and a shoulder 66. The piston installation device 16 is composed of a plurality of deflectable flexible fingers 94 arranged with same distances. The fingers 94 are each composed of a coming surface 100 connected to a stem 96 by means of spirally extending shoulders 102. The fingers 58, 94 of the installation devices 15, 16 passes through a hole 44 and a boss 48, while being deformed inward and reset, and shows fixation function.