a universal head having a rotary part and rotatably installed in a ram body;

a cable having one side connected to a rotary part of the universal head, and the other side connected to a supply source;

a rotation unit disposed on the rotary part of the universal head and configured to wind or unwind the cable while rotating in conjunction with a rotation direction and a rotation angle of the rotary part of the universal head; and

a movement unit disposed in the ram body so as to rectilinearly reciprocate to compensate for a change in length of the cable remaining after being wound around or unwound from the rotation unit in accordance with a rotation direction and a rotation angle of the rotation unit,

wherein the rotation unit comprises:

a main body part detachably installed on the rotary part of the universal head and extending in a length direction so that the cable is wound around or unwound from an outer peripheral edge of the main body part;

a through part formed through the main body part; and

a flange part protruding from the outer peripheral edge of the main body part and configured to guide a process in which one side of the cable having passed through the through part is wound around or unwound from the outer peripheral edge of the main body part in conjunction with a rotation of the rotary part of the universal head.