Pipe joint structure and method of assembling the same

In a pipe joint structure, a second screw thread (35) formed on an outer circumference end of a joint member (24) is screwed deep into a first screw thread (29) formed on an inner circumference of a cylindrical joint fitting member (23) whose axial end is bonded to a common rail body (20) so that a second flat surface (36) at an axial end of the joint member (24) is pressed against a first flat surface (27) on an outer circumference of the common rail body (20) to form a fluid tight sealing surface (37) therebetween in a state that a fluid passage (34) which is provided in the joint member (24) and is opened to the second flat surface (36) communicates with a through-hole (26) which is provided in a circumferential wall of the common rail body (20) and is opened to the first flat surface (27). Accordingly, even if a position of the joint fitting member (23) to the common rail body (20) is slightly shifted, fluid tight sealing between the first and second flat surfaces (27,36) is assured.