A printing plate discharging method and a printing plate discharging device can quickly and reliably discharge a printing plate from a surface plate, which printing plate has been placed in a state wherein one end portion of the printing plate projects from the surface plate, without making an exposed face of the printing plate dirty or scratched. At a discharging mechanism section of an automatic exposure device, a temporary support arm corresponds with the one end portion of the printing plate, which end portion projects from on the surface plate. The temporary support arm is raised higher than the surface plate by a moving stage moving and a roller thereby abutting against a projecting portion of the temporary support arm. Thus, the temporary support arm lifts up the one end portion of the printing plate. In this state, a plate discharging hook engages the one end portion of the printing plate (a lifted portion) and pushes the printing plate toward another end portion of the surface plate. Thus, the printing plate can be discharged from the surface plate.