an automatic levelling device for attachment to a ladder to allow the ladder to be used on an uneven supporting surface . the levelling device includes a downwardly opened u - shaped tubular member which guidably supports therein a ball chain connecting element . slidable within the open ends of the tubular member and attached to opposite ends of the connecting element are extendable legs . a locking means is connected to the tubular member and is adapted to cooperate with the ball chain to provide positive locking of the chain when the extendable legs are in the proper position to maintain the ladder in a vertical orientation . the ball chain when locked in the locking means can not be unlocked unless weight is removed from both supporting legs .