This locking system includes a male cylindrical end and a female tubular cylindrical end inside of which the male cylindrical end is to be inserted for coupling. A locking groove is hollowed in the outer surface of the male cylindrical end. The female tubular cylindrical end is bored on the side with a through-opening inside of which is arranged a mobile locking element which protrudes inside the female tubular cylindrical end in the locking groove of the male cylindrical end. A locking ring is mounted to rotate freely on the outer surface of the female tubular cylindrical end opposite the through-opening this ring having an inner surface wherein a recess having an ortho-radially variable depth enables the locking/unlocking of the mobile locking element against the locking groove depending on the ring's position. The locking groove extends in the axial direction of the male cylindrical end from a free end thereof.