There is provided an automatic document feeder, comprising: a document tray; an output tray; a first rotating body that ejects the document to the output tray; a second rotating body that ejects the document to the output tray; a reversing mechanism that reverses a carrying direction of the document which passed the reading portion to carry again the document to the reading portion; a sinking mechanism that sinks the document into a position between a bottom of a document already stacked on the output tray and a surface of the output tray; and a switching mechanism configured to switch between a first motion of carrying the document to the first rotating body and a second motion of carrying the document to the second rotating body, in accordance with whether the reversing mechanism is activated.