Abstract: A levelling device for ladders has a pair of locking bars (24, 32, 51, 52) pivotally mounted on the ladder (28, 31, 42). A support arc (16, 33, 48), having feet (19, 34) at each end, passes through apertures (50) in the locking bars (24, 33, 51, 52). Springs (25, 46) interconnecting each locking bar (24, 32, 51, 52) and the ladder (28, 31, 42) urge the locking bars (24, 32, 51, 52) to an unlocked position where the support arc (16, 33, 48) is free to pass through the apertures (50). When weight is applied to the ladder (28, 31, 42), the locking bars (24, 32, 51, 52) are urged to a locked position, against the springs (25, 46), where the sides of the apertures (50) engage the support arc (16, 33, 48) to lock it against further movement. By adjustment of the support arc (16, 33, 48), the feet (19, 34) may be raised or lowered to accommodate any irregularities in the support surface so that the ladder (28, 31, 42) will stand vertically.