To provide a waste plate box with superior operability such that even a large-sized or wide printing plate can be made compact and easily disposed of into a waste box of normal size outside the waste plate box.

A waste plate box 10 attached detachably to a printing device 1 has a first box part 12 with a first discharge opening 12a and a second box part 13 with a second discharge opening 13a connected rotatably by a hinge 22 nearby both the discharge openings. The first discharge opening and the second discharge opening are connected together and closed, and attached to the printing device when a plate is discharged. When the plate is disposed of, the first box part and the second box body are taken out of the printing device and rotated around the hinge to open the first discharge opening and the second opening, and the waste plate S is dropped and disposed of.