An automatic document feeder (ADF) used in a facsimile machine, photocopier or the like. A sheet path from a sheet inlet to outlet is defined by lower, intermediate and upper frames of the ADF. The sheet path is generally shaped like nullCnull when viewed laterally. The intermediate frame has a pivotable member that can be opened and closed, and a guide member for guiding a sheet passing over a platen glass. An elastic member is provided for biasing the guide member on the platen surface from a turning portion of the C-shaped sheet path. Therefore, it is possible to maintain a clearance between the platen surface and guide member and prevent the sheet from flapping. A retard roller is removably supported by the pivotable member so that replacing and maintenance of the retard roller is simplified. Further, the pivotable member is a one-piece element and made from resin. A plurality of ribs extending in a sheet feed direction are provided near the sheet inlet and/or outlet so that the weight of the automatic document feeder is reduced and movements of the sheets are facilitated.