A counter ejector disposed at a downstream part of a box former, the counter ejector including a hopper that receives a sheet-shaped corrugated board box being transferred from an upstream side and fallen; and a blower that downwardly blows air to a hopper from above the corrugated board box, wherein the blower is capable of changing a blowing area to be blown along a transfer direction of the corrugated board box, and blows air to the blowing area corresponding to at least the front-end portion and the rear-end portion of the hopper in the transfer direction if the corrugated board box has a possible maximum size in the transfer direction.