A platform ladder apparatus (2) has a transport position and a use position in which the apparatus is arranged to lean against a wall (W) for performing work at an elevated level. The apparatus (2) has a ladder (4) and a working platform (20). A proximal side of the platform is pivotally connected at an upper end of the ladder such that it may be pivoted towards the ladder (4) to a stowed position essentially parallel to the ladder (4). The apparatus further comprises a pair of wall support arms (80) for stabilizing the apparatus in the use position in relation to the wall. The wall support arms (80) are connected to the platform (20) for movement between a stowed arm position in which the arms (80) project out from a distal side (24) of the platform (20) thereby preventing use of the apparatus, and a stabilizing arm position in which the arms (80) project sideways from the platform (20) in opposite lateral directions, respectively, for stabilizing the apparatus (2) in relation to the wall (W).