To provide a pin capable of holding both an upper fly and a lower fly.

A pin (an example of a tentative name) 15 for fastening flies is of an S-shaped pin type, which holds the upper fly 1d and the lower fly 1f of a white shirt to thereby fasten both of the flies, so that even when the second button is unfastened, the upper fly can be prevented from fully opening up to the third button. Thus, even when the second button is unfastened to open the flies, moderate open feeling and the good appearance can be achieved.