Fastening device for a bracelet , said fastening device being suited to be connected to a first terminal area and to a second terminal area of said bracelet , said fastening device comprising a first laminar element and a second laminar element mutually hinged to each other and suited to be arranged in a closed operating configuration, in which they are superimposed, and in an open operating configuration, in which they are at least partially parted, said first laminar element comprising a first area suitable for connection to said first terminal area of said bracelet and a hinge area where it is hinged to said second laminar element , said second laminar element comprising a hinge area where it is hinged to said first laminar element , said fastening device further comprising adjusting means suited to adjust the distance between said first terminal area and said second terminal area of said bracelet , said adjusting means comprising: - a coupling element suited to be connected to said second terminal area of said bracelet ; - first connection means associated with said coupling element ; - second connection means defined in said second laminar element ; said first and said second connection means being suited to cooperate in order to arrange said coupling element in several positions with respect to said second laminar element , further comprising holding means suited to maintain said coupling element coupled with said second laminar element , and characterized in that said holding means comprise an auxiliary laminar element (82; 82'; 82"; 82′′′) hinged to said second laminar element , said auxiliary laminar element (82; 82'; 82"; 82′′′) being suited to be arranged in a closed holding position on said second laminar element and said coupling element , and in an open position suited to allow said coupling element to be disconnected from said second laminar element . a first laminar element and a second laminar element mutually hinged to each other and suited to be arranged in a closed operating configuration, in which they are superimposed, and in an open operating configuration, in which they are at least partially parted, said first laminar element comprising a first area suitable for connection to said first terminal area of said bracelet and a hinge area where it is hinged to said second laminar element , said second laminar element comprising a hinge area where it is hinged to said first laminar element , said fastening device further comprising adjusting means suited to adjust the distance between said first terminal area and said second terminal area of said bracelet , said adjusting means comprising: - a coupling element suited to be connected to said second terminal area of said bracelet ; - first connection means associated with said coupling element ; - second connection means defined in said second laminar element ; - a coupling element suited to be connected to said second terminal area of said bracelet ; - first connection means associated with said coupling element ; - second connection means defined in said second laminar element ; said first and said second connection means being suited to cooperate in order to arrange said coupling element in several positions with respect to said second laminar element , further comprising holding means suited to maintain said coupling element coupled with said second laminar element , and characterized in that said holding means comprise an auxiliary laminar element (82; 82'; 82"; 82′′′) hinged to said second laminar element , said auxiliary laminar element (82; 82'; 82"; 82′′′) being suited to be arranged in a closed holding position on said second laminar element and said coupling element , and in an open position suited to allow said coupling element to be disconnected from said second laminar element . <EOS>