Abstract: A service elevator, designed to carry persons up or down along a building wall or other structure, comprises a ladder secured to that structure and a carriage on which an endless conveyor band is supported. The band has projecting dogs engaging the rungs of the ladder which are held between a first stringer of circular cross-section and a second stringer of rectangular cross-section. The band-supporting frame has sleeves slidably engaging the first stringer and roller pairs bracketing the second stringer. A second conveyor band, serving as a standby for the working band, corotates therewith and has dogs slightly offset from those of the latter for dropping onto the rungs when the working band fails.