A fluid apparatus unit structure in which a uniform tightening force is easily applied over the entire periphery by tightening a plurality of fastening members to obtain an advantageous sealing performance is provided. In s fluid apparatus unit structure in which plural fluid apparatus components that are connected via flow paths are collected together and integrated onto a base member, a casing member for the fluid apparatus components is partitioned into plural members in the base member mating direction, a female threading portion assembly (19) in which plural nut portions (18a) that form female threading portions that communicate in the mating direction are integrated by a linking member (18b), is fit and installed on base side partitioned members of a casing member that is disposed at a position in close contact with a base member or a base members, and with base side member interposed therebetween, different fastening members are threaded and tightened from both sides of the nut portion (18a).