An automatic document feeder includes a guide member which has a flexible thin piece. A plurality of recesses are formed in a free end of the guide member in spaced-apart relationship in a width direction to provide the plurality of recesses and a plurality of protrusions adjacent to the recesses. The recesses and protrusions are formed and disposed so that both side edges of original documents of various standard sizes may pass tip portions or outside edge portions of the protrusions. By this, both side edges of the original documents are without foil scopped by the protrusions. Accordingly, both edges of original documents do not enter the interior most portions of the recesses and thus a paper jam does not occur.