To provide a coupling structure enhanced in tightness and having less looseness.

The coupling structure includes: a first member 21 having a hole a; a second member 22 having a hole b; a female-thread cut body 4 having a cylinder body 4a wherein a female thread is cut on its internal surface and a flange section 4b overhanging to the periphery of the cylinder body 4a from the end of the cylinder 4a; and a male-thread cut body 5 wherein a flange section 5a is formed at its one end and a male thread 5b screwed with the female thread of the female-thread cut body 4 is cut. The structure is configured such that at least either of the first member 21 or the second member 22 has a plurality of holes, and that the hole a of the first member 21 is made to coincide with the hole b of the second member 22, the female- thread cut body 4 and the male-thread cut body 5 are inserted into the hole a of the first member 21 and into the hole b of the second member 22, respectively, and the female-thread cut body 4 and the male-thread cut body 5 are clamped to couple the first member 21 and the second member 22. Also in the structure, the tip of the cylinder body 4a of the female-thread cut body 4 reaches the hole b of the second member 22, and the cylinder body 4a of the female-thread cut body 4 is made to abut against the wall face of the hole a of the first member 21 as well as against the wall face of the hole b of the second member 22.