Abstract: A fastening device for a plug, which is plugged into a jack with two ends that each have a threaded hole, the fastening device comprising: a left bolt and a right bolt, each having a main body, a male thread, inserted in the threaded holes of the jack, and several transversal holes; and a securing wire, having two ends, two fastening sections at the two ends, which are inserted into a transversal hole of the left bolt and a transversal hole of the right bolt, two connecting sections, respectively continuing from the fastening sections, and a holding section between the two connecting sections; wherein the securing wire has a securing position for securing the plug on the jack and a releasing position for removing the plug from the jack and is switched between said securing and releasing positions by turning around the fastening sections.