PURPOSE: To provide an automatic document feeder which can prevent the staining of a carrying belt from being read by an image forming device.

CONSTITUTION: As to the automatic document feeder which carries a document G in a contact glass 21 through the carrying belt 10 and carries the document G out of the contact glass 21 after an image is read out; a pair of sheet carrying rollers 16, etc., alternately carrying in and out a white sheet S at least having the size of document length with respect to the contact glass 21, a guiding board 17, etc., which allows the document G and the sheet S to be carried to meet each other, such an electrostatically charging means as an electrostatic charger 9 electrostatically charging at least either the sheet S or the document G before meeting, such a synchronizing carrying means as a pair of resist rollers 8 and the pair of sheet carrying rollers 16 synchronously carrying the sheet S with respect to the document G in a state where the document G and the sheet S have a specified phase difference on a front end side at the time of carrying the document and the sheet S out, and a separation lug 11 separating the document G and the sheet S carried out of the contact glass 21 are provided.