To automatically switch a plate material exit/entrance of a plate material jacket containing the material therein.

At the time of supplying a printing plate, an opening end 9c of a cover sheet 9 of a plate material jacket 6 is sucked and lifted by a suction pad 104. Thus, a switching cover 13 formed at the end 9c is automatically drawn upward from a switching cover locking hole 14 of a base sheet 8 to open a plate material exit/entrance 7. After the plate is discharged, an end of the cover 13 is curled down by a guide plate 124 to guide the cover 13 by the plate 124. Then, the cover 13 is automatically inserted from above into the hole 14, and locked to lock the entrance 7 in a closed state.