A bill processing device comprising: a loading unit that feeds a bill having a pair of serial number information; a reading unit that is configured to read the pair of serial number information from the fed bill; a determining unit that is configured to determine whether at least a portion of the pair of serial numbers match each other; a stacking unit that is configured to stack the bill in a case where the determining unit has determined that the at least a portion of the pair of serial numbers match each other; a reject unit that is configured to receive the bill in a case where the determining unit has determined that the at least a portion of the pair of serial numbers do not match each other; an image data capture unit that is configured to capture image data of an unreadable bill whose serial number information is unreadable by the reading unit; a display unit that is configured to display the image data of the unreadable bill; characterized by an input unit that is configured to receive an input of serial number information from an operator who has visually confirmed the unreadable bill; and a compositing unit that is configured to composite, on the image data of the unreadable bill, image data showing the input serial number information, to generate composite image data; wherein the display unit displays the composite image data, the input unit receives, as the input of the serial number information, an input of serial number information including a symbol indicating an unclear part, and the compositing unit composites, on the image data of the unreadable bill, image data showing the input serial number information including the symbol. a loading unit that feeds a bill having a pair of serial number information; a reading unit that is configured to read the pair of serial number information from the fed bill; a determining unit that is configured to determine whether at least a portion of the pair of serial numbers match each other; a stacking unit that is configured to stack the bill in a case where the determining unit has determined that the at least a portion of the pair of serial numbers match each other; a reject unit that is configured to receive the bill in a case where the determining unit has determined that the at least a portion of the pair of serial numbers do not match each other; an image data capture unit that is configured to capture image data of an unreadable bill whose serial number information is unreadable by the reading unit; a display unit that is configured to display the image data of the unreadable bill; characterized by an input unit that is configured to receive an input of serial number information from an operator who has visually confirmed the unreadable bill; and a compositing unit that is configured to composite, on the image data of the unreadable bill, image data showing the input serial number information, to generate composite image data; wherein the display unit displays the composite image data, the input unit receives, as the input of the serial number information, an input of serial number information including a symbol indicating an unclear part, and the compositing unit composites, on the image data of the unreadable bill, image data showing the input serial number information including the symbol.