An image forming device includes an image carrier carrying an image, a transfer device including paired transfer members that transport the image carrier and a recording medium, a grounded guide member that guides the recording medium to a transfer region, and a transfer power source that produces an electric field in the transfer region causing the image to be transferred onto the recording medium. The transfer power source includes a first transfer power source that imparts a first transfer voltage to one of the paired transfer members, and a second transfer power source that, when the recording medium has a predetermined resistance value or less, or is of low resistance having a conductive layer along a medium substrate face, imparts a second transfer voltage of opposite polarity and having an absolute value less than or equal to the first transfer voltage to the other of the paired transfer members.