An auto document feeding device causes an original document passing through an OUT path and an original document passing through an IN path to flow together with overlap a trailing edge of a preceding original document and a leading edge of a following original document. Before the original documents reach to a READ document glass, the auto document feeding device comprises a separating unit configured to separate an overlapping portion of the original documents. The auto document feeding device reduces a distance between the preceding original document and the following original document passing on the READ document glass to nearly 0 mm.