To provide an automatic document feeder capable of reducing an installation space of a drive device, reducing the number of components, such as a drive motor, to have a simple configuration, and also, reducing an operation noise to improve noise reduction, and to provide an image forming apparatus including the automatic document feeder.

An automatic document feeder includes a switchback means having: a branch guide for switching a conveying passage to read a second surface after reading a first surface of a document; and a pair of switchback rollers for resending the document to a conveying means after switching the conveying passage through the branch guide. The switching of the conveying passage of the branch guide, and the opening/closing of a nip between the pair of switchback rollers are performed by one driving means, and thereby, the installation space of the driving means can be reduced.