An image forming device includes: an image forming part that forms an image on a transfer medium; a conveyance part that conveys the transfer medium; and a hardware processor that controls the conveyance part, receives a result of reading by an image reader, which reads an image on the transfer medium passing through the image forming part, and determines whether an image on the transfer medium is normal, wherein the hardware processor can perform control of sorting, by a sorting part that can perform sorting of a transfer medium according to a result of the determination, a transfer medium determined to have a normal image and a transfer medium determined to have an abnormal image, and can further perform control of previously grasping analysis time in the determination and suspending conveyance of the transfer medium at a conveyance position at or in advance of a sorting position.