A device for unfastening fasteners includes an operation device, a cable unit and a working unit. The cable unit is connected between the operation device and the working unit. The operation device includes a first part and a second part pivotably connected to each other by a pivot. The first part includes a first extension with a first hole. The second part includes a second extension with a second hole. A first slot communicates with the first hole. A second slot communicates with the second hole. The cable unit includes a cable and a sheath. The cable extends through the first and second holes via the first and second slots, and connected with an end piece which contacts the first extension. A stop member is mounted to the first extension to close the first slot. The cable is separated from the operation device easily without causing damage to the cable.