To strongly attach a cap body made of synthetic resin to the leg part and resting frame of a chair and a desk, or the like, and to easily detach it.

The cap body 25 is composed of a shaft part 27 to be fitted to the leg pipe P of the chair and the desk, or the like, and a head part 26 to be exposed from the leg pipe. Then, an operation hole 30 for fitting an attaching shaft member 35 is made to pass through the axial direction center of the cap body 25, a slit-like division groove 31 communicating with the operation hole is formed in an axial direction at the shaft part 27 and the shaft part is enlarged in a radial direction through the division groove 31 and brought into press contact with the inner wall of the leg pipe P accompanying the fitting of the attaching shaft member 35 to the operation hole 30.