An external fixator for fixing bones includes a coupling member, a plurality of ball joints, each ball joint comprising a pin to be inserted into a bone, a rotary member in form of a ball, a supporting member in which a first supporting member and a first thread for supporting the ball rotatably are formed, and a tubular fastening member that contains the ball and that has openings at the opposite ends, the tubular fastening member is provided at one end with a second thread corresponding to the first thread. The tubular fastening member is provided at the other end with a second supporting portion for pushing the ball against the first supporting portion when the second screw is driven into the first thread, wherein the pins and the coupling member are fixed to the supporting member and the rotary member.