PURPOSE: To enable two duct joints with continuous irregularities on an inner wall to be easily connected, using a member of simple constitution.

CONSTITUTION: Both ends of a cylindrical body are used as insertion sections 20a for coupling to a duct, and coupling projections 22 having a larger outer diameter than other sections are formed at the predetermined positions of the insertion sections 20a. In addition, the sections 22 and the vicinity thereof are so formed as to have elasticity for flexing inward due to external pressure. The coupling projections 22 are engaged with an irregular section inside the duct, upon coupling the insertion sections 20a and, therefore, good coupling state can be maintained between a slip joint and a duct only via a coupling work. Furthermore, a seal material is fitted to both ends of the center large diameter section of the slip joint and, therefore, high sealing quality can be kept between the joint and the duct, thereby ensuring the high sealing quality of a joint section.