A seal cap (20) is formed of an elastically deformable material and includes a cap portion (21) that closes a passage port, a grip portion (24) that can be grasped, and a joining portion (26) which integrally joins the cap portion (21) and the grip portion (24). The joining portion (26) has a bolt insertion portion (23) through which a stud bolt (15) can be inserted. The grip portion (24) is formed on a side of the bolt insertion portion (23) that corresponds to the cap portion (21). The joining portion (26) is formed between the bolt insertion portion (23) and the cap portion (21) and is provided with a cut (27) which communicates with the bolt insertion portion (23). The cut (27) allows the cap portion (21) to be bent and deformed by the contact between the cap portion (21) and the stud bolt (15) during pulling out of the seal cap (20) from a connection portion (12).
