A levelling device for ladders (1) and the like. Aperture lugs (9), adapted for attachment to the bottom ends of uprights, stiles or legs (2) of a ladder (1), trestle, etc., are slidably mounted on an arcuate support bar (13), and biased to a non-locking or freely slidable position. On application of weight to the ladder (1), the apertured lugs (9) pivot to an locking position. In one embodiment, each of the aperture lugs (9) is formed with extension members or fingers (16) with abutment surfaces extending parallel to the plane of the ladder (1) which tangentially engage the sides of the support bar (13) when the apertured lugs (9) are in lock position to prevent or limit any tiltable movement of the support bar out of the plane of the ladder. In another aspect of the invention, the lugs (9) are provided with non-circular apertures and the support bar (13) is formed with a complementary non-circular cross-sectional configuration, such as triangular, square, etc., which configurations prevent rotation of each apertured lug (9) around the support bar (13), and thus prevent or limit tilting of the support bar (13) out of the plane of the ladder (1). The levelling device of the present invention may be used on any number of different sizes of ladder (1) to provide stable and safe levelling of the ladder (1).