A pair of adherence rollers (24,25) are attached to a carriage (4) of a stacker crane (2) through rocking bases (26). The adherence rollers (24,25) are biased upwardly by springs (30) to adjust wheel pressures applied to the rollers. The rollers (24,25) contact the bottom surface of the traveling rail (12) under the wheel pressures determined by the springs (30) so that suitable wheel pressures can be applied to drive wheels (34) during acceleration.