A safety locking device 18 for a quick hitch/coupler 10 of an earth working machine. The safety locking device 18 has a locking element 21 which is biased into a locking position to automatically lock a front pin of an implement when it is engaged in the hook 14 of the coupler 10. The safety locking device 18 has an hydraulic operable mechanism to move the locking element 21 to an unlocking position. The hydraulic supply to the safety locking device 18 is independent of the hydraulic supply to a locking mechanism 16 of the coupler 10.