A READING UNIT (3) PLACED ON THE INNER SIDE OF A U-SHAPED FEED PATH (12) THAT FEEDS A DOCUMENT IS FORMED SUCH THAT THE HEIGHT-AXIS DIMENSION OF SAID READING UNIT DECREASES IN A DIRECTION EXTENDING TOWARD A SIDE HAVING A PAPER DELIVERY TRAY (11). CONTACT GLASS (20), A LIGHT SOURCE AND A FIRST MIRROR (24) ARE PLACED IN THE READING UNIT (3) AT AN END PORTION OF THE SIDE HAVING THE PAPER DELIVERY TRAY (11). MULTIPLE REFLECTING MIRRORS (25, 26 AND 27), A LENS (28) AND A PHOTOELECTRIC CONVERTER ELEMENT (29) ARE PLACED FURTHER FROM THE PAPER DELIVERY TRAY THAN THE FIRST MIRROR (24) IN THE READING UNIT. THIS STRUCTURE ENABLES THE READING UNIT PROVIDED IN A DOCUMENT FEEDER TO BE MORE COMPACT WHILE ENSURING THE REQUIRED LIGHT PATH LENGTH, AND ENABLES THE ENTIRE DOCUMENT FEEDER TO BE MORE COMPACT.