An image processing apparatus includes an auto document feeder, and can simultaneously scans both sides of an original at a fixed scan position during one-time original feed. The image processing apparatus further includes a first scanning unit that scans a front side of the original in a single-sided scan and a double-sided scan; and a second scanning unit that scans a back side of the original in the double-sided scan. In the double-sided scan, the first scanning unit and the second scanning unit scan the original by using the same scaling method. The first scanning unit uses different scaling methods between the single-sided scan and the double-sided scan based on an original scan condition.