The equaliser for a ladder assembly (1-14) consists of at least one extension member, abutting the ladder upright and formed by a profiled section. In its adjustable position the extension member has a securing and/or locking device acting w.r.t. the ladder upright. At the lower end the extension member has a foot of profiled, elastic, slip-preventing material. To the extension member is associated a slide guide connectable to the ladder upright, and a device securing the extension member on the slide guide. Pref. the extension member is made of a hollow profiled material with at least slit apertures.