The image forming apparatus includes a printing device, an image reading device, a job management unit, and a document detection processing unit. The image reading device reads an image in a predetermined range in which a document can be arranged, as a read image. The job management unit acquires a front side image and a back side image of a card document, and prints the front side image and the back side image on both sides of a print sheet using the printing device. The document detection processing unit specifies a document image area of the front side image and a document image area of the back side image. The job management unit selects a larger size as the common image area size when a difference in size between the document image areas of the front side and the back side exceeds a predetermined threshold.