Abstract: A stablizing device to be connected on the outer sides of the side pieces of a ladder has a lower leg pivoted on a lower part of the side piece and pivoted at its upper end to an upper leg part which has a locking member for releasable locking on the side piece. By adjustment of the upper leg part, the leg parts can be braced against the ground or against a vertical wall surface. This device leaves the rungs of the ladder unobstructed and the upper leg part may be freely slidingly connected on the side piece so that the knees can readily be adjusted independently to allow the ladder to be stabilized on uneven ground. There is disclosed an arrangement in which a lever on the upper leg part engages a toothed rack on the side piece and lifts the ladder bodily upwards a small distance as the lever is pressed inward to the side of the ladder.