Provided is a clamp for fastening a portable electronic device. The clamp comprises two spring biased sliding arms and a spring biased trigger member. Pushing the trigger member toward the body will move the shuttle member upward to unlock both arms for extending thereafter. In response to sandwiching the device between the arms releasing the trigger member will push the trigger member outward and the shuttle member downward respectively for locking the ridges. In a case of the device having its ports provided at one side or both sides thereof, two central, rectangular openings of the arms are adapted to allow the ports to dispose therein for causing no interference to a normal operation of the fastened device. A distance between both arms can be adjusted by sliding one arm toward or away from the other arm or sliding both arms toward or away from each other.