To solve a problem that since a small diameter part is extended and provided in an axial center direction on one end side of a pipe member, a gap between pipe members is forcibly expanded, making connection difficult, and backlash is produced between the small diameter part and a pipe member with the small diameter part inserted therein, so that the pipe member raised horizontally tends to droop anyway.

An engagement protrusion 29 is provided at a small diameter part 11 of a pipe member 7, an engagement hole 37 is formed on another end side of the pipe member 7, a tapered part 19 diametrically reduced gradually from the another end side to one end side is formed at a middle part of the pipe member 7, and the small diameter 11 side is totally tapered. If a pipe member 7A is inserted into a pipe member 7B, the engagement protrusion 29 and the engagement hole 37 are engaged, and an outer surface of the small diameter part 11 of the pipe member 7A and an inner surface of the pipe member 7B are brought into press contact annularly. Thereby, even if a length dimension (L1) of the small diameter part 11 is set shorter than conventional ones, the pipe member can be stably supported when placed laterally in air. Further, the pipe member hardly droops than conventional ones as the small diameter part 11 is short, also facilitating connection work.