To easily attach a faster to an attachment hole 21, or to detach it therefrom.

The faster 10 is attachable to and detachable from the cylindrical attachment hole 21 with a side hole 22 formed on a side surface, and is provided with: a cylindrical barrel part 11b insertable to the attachment hole 21; a head part 11a not insertable to the attachment hole 21 provided at the barrel part; a hole part 14 wherein a lower end is closed by a bottom part of the barrel part 11b and an upper end is opened with a head part opening part 14a provided at the head part 11a; and a barrel part opening part 14b for communicating the hole part 14 with outside at a position corresponding to the side hole 22 while the fastener 10 is mounted on the attachment hole 21. In the hole part 14, a flexible engaging rod 12 is inserted with its end protruding from the head part opening part 14a in a normal state, and an elastic body is provided between another end of the engaging rod 12 and a bottom surface of the hole part 14. The engaging rod 12 has a branch part 13 branching to protrude its end from the barrel part opening part 14b in the normal state.