A cover includes a cover body and a covering portion. The cover body can include an opening edge exposing a part of a distal structure portion, an annular portion surrounding a periphery of the distal structure portion, a proximal edge, a dividing portion provided in the annular portion in a manner to define a slit that is continuous with the opening edge portion and the proximal edge portion, and an overlapping portion. The dividing portion includes a first cylindrical wall portion, and a second cylindrical wall portion. The first cylindrical wall portion and the second cylindrical wall portion overlap at least partly in the overlapping portion. The covering portion is configured to cover a part, where at least the dividing portion is provided.
