An improved locking device is provided for one a livestock head gate in which two doors rollingly engaged on an overhead guide shaft for rolling movement of said two doors toward one another into a closed position bracing a livestock animal between said doors and away from one another into an open position releasing said livestock animal. Primary and secondary shaft-receiving and locking members have respective first and second through-holes therein for receipt of the overhead guide shaft. A spring-receipt member is fixed to the primary shaft-receiving member for cooperation with a spring that tilts the primary shaft-receiving member into a locking position. The secondary movable locking member is retained beside the primary locking in a manner enabling both tilting therewith and displacement relative thereto so as to bite onto the shaft at the perimeter of the second through-hole in the locking position.