A document feeder includes: an inlet; an outlet; an input transfer path configured to guide a document during transfer from the inlet passed a scanning point to an end point positioned above the inlet; an intermediate transfer path configured to guide the document during transfer from the end point passed the scanning point to the end point again; an output transfer path configured to guide the document during transfer from the end point passed the scanning point to the outlet; a sensor disposed at downstream of the scanning point; and a controller determine whether the document transfer, based on the signal of the sensor.