An image forming apparatus and a computer system having an efficient communication system are achieved. The image forming apparatus etc. is provided with an antenna that is capable of wirelessly communicating both with the developing-unit element of the developing unit attached to the developing unit attach/detach section and with the photoconductor-unit element of the photoconductor unit attached to the photoconductor unit attach/detach section. Further, when R is an outermost diameter of a path traced by the developing units and r is an outermost diameter of a path traced by the elements when the rotating member is rotated with the developing units attached to the attach/detach sections, then a relationship R>r is satisfied.