Document feeder for efficiently supplying originals and storing originals in a discharge stacker after reading

In a document feeder, a length of a discharge path from a reading position to a discharge position is longer than a length of a supply path from a feeding position to the reading position. An idling discharge position is disposed, where the distance with the discharge position through the discharge path is shorter than a distance between the feeding position and the reading speed switching position. A control device controls driving of registration rollers, conveyor rollers and discharge rollers simultaneously when a trailing edge of an original reaches the discharge idling position of the discharge path by the discharge rollers while the discharge rollers is stopped. The document feeder efficiently supplies originals sequentially to the reading position, stably reads the image of the original without discharging a previous original during a reading, and aligns and stores the originals in a discharge stacker.