An intermediate guide member is provided attachable and removable between a head portion and a supporting frame of a stocker for printing plates. A number of intermediate guide members is an element to set a time of starting downward movement of hooks supporting a leading end of a printing plate. Three conditions in accordance with lengths of non-detection times are set for detecting the printing plate to judge authenticity of the detection. When the hooks reach vicinities of stoppers provided at supporting bars of a reversal unit, the hooks swing, are pulled-in from above the slope, and transfer the printing plate to the stoppers. Thereafter, by rotating the supporting bars and the stoppers integrally around a shaft, the printing plate is pivoted over toward a back plate, and a lower end of the printing plate is transferred from the stoppers to a receiving plate without damaging the printing plate.