The fastening device of the present invention includes a base, two pawl shanks and two positioning rods. The base is formed with two hook portions and two base positioning holes. Each pawl shank is formed with a pawl positioning hole, and each pawl shank includes a pawl section and a hook section. Each positioning rod inserts in one of the base positioning holes and the pawl positioning hole of one of the pawl shanks, such that the pawl shanks are pivotable about the positioning rods respectively. Each hook portion and its corresponding hook section define a tube clamp space, and the pawl sections define a pad clamp space. The fastening device further includes a means for narrowing the tube clamp spaces and the pad clamp space.