A sheet reader reads the entire sheet which is transported. Based on the reading, a controller generates region classification image data for distinguishing between a region of the sheet and a region other than the sheet. The controller performs comparison processing in which reference image data that is the region classification image data of a first sheet in a print job and comparison target image data that is the region classification image data for another sheet are compared. The controller determines whether or not a sheet corresponding to the comparison target image data is abnormal.