To provide an inexpensive joint part structure capable of stably connecting members such as steel pipes.

A joint part structure 2 includes a pair of joint members 4 and 5 relatively movable mutually in predetermined directions for overlapping each other at predetermined positions in the moving directions, and a movement inhibiting pin member 6 for penetrating through a pair of insertion holes 15 and 16 formed in the joint members, respectively, and continuous with each other in the overlapping direction. A tapered fitting-in part 18 is formed on the outside face of the movement inhibiting pin member 6 and a tapered fitted-in part 17 to be fitted in the fitting-in part 18 is formed over the inner peripheral faces of both insertion holes 15 and 16. In the state that the outside face of the fitting-in part 18 closely contacts the inside face of the fitted-in part 17, the movement inhibiting pin member 6 penetrates through the insides of both insertion holes 15 and 16.