To provide a cap for a cylindrical member, which enables holding of a tool.

A cap 1 closes an end of a cylindrical member 3 to hold a tool 5 having a rod-like tool body part 5a provided with a tool extension part 5b extended in a direction crossing an axial direction. The cap 1 includes a body part 11 that is attached to an end opening of the cylindrical member 3, an insertion hole 23 that is formed in such a shape as to penetrate in the axial direction of the body part 11 and through which the tool body part 5a is inserted, and a storage part 25 that is positioned on the side of the end opening and that communicates with the insertion hole 23 to accommodate the tool extension part 5b.