An image reading apparatus for use in an image forming apparatus includes a document glass installed on an upper side of the image reading body on which a document is placed; an image reading sensor installed under the document glass for stopping after being transferred to a predetermined position or for reciprocating in a straight direction parallel to the document glass; a cover for opening and closing the upper surface of the document glass; an automatic document feeder (ADF) for feeding the document to the position to which the image reading sensor is fixed; a document discharging plate for discharging the document fed through the automatic document feeding unit; first and second guide members for guiding to allow the document fed through the automatic document feeding unit to be discharged to the document discharging plate, the first and second guide members being installed at a predetermined interval to expose the document toward the image reading sensor; and a guide film installed to cover the interval between the first and second guide members for guiding to allow the document to be discharged to the document discharging plate. By this structure, a size of the image forming apparatus can be reduced.