A memory device memorizes, in association, possessor identification information, which is recorded at recording mediums carried by authorized users of an image forming device, and inputter identification information corresponding to the possessor identification information. An information retention device memorizes image information and inputter identification information transmitted from an image formation instruction device. A reading device reads possessor identification information from a recording medium. If it is determined that this possessor identification information has been memorized at the memory device, an image formation section reads image information that is associated with inputter identification information that is associated with the possessor identification information, and implements image formation. If not, an output section outputs the possessor identification information. When the possessor identification information is inputted through an input section, a registration section registers the possessor identification information and inputter identification information by memorizing them in association at the memory device.