To prevent a pin member from being unexpectedly detached and lost by providing a lock mechanism at the time of engaging a pin, to improve aesthetic appearance by providing the sense of unity with an accessory itself, to improve operability and durability as a fastener and to perform mass- production at a low cost by simplifying a structure.

A sliding body 2 provided with a knob part 3 is provided inside a cylindrical fastener main body 1 freely slidably through a spring 5. A pin engaging part 4 is provided in a direction crossing with the sliding direction of the sliding body 2. Further, the tip part of the pin member 9 provided by pivotally attaching 14 the rear end part 13 of the accessory main body 12 is engaged with the pin engaging part 4. On the other hand, this fastener is provided with a double lock mechanism for releasing the engagement of the pill member 9 and the pin engaging part 4 by sliding the sliding body 2 while pressing the pin member 9.