In order to promote the utilization of a display panel as an operation panel, when detecting a communicable terminal device (9) (S1), a CPU (10) requests the terminal device (9) to transmit panel information (S2), and determines, on the basis of the panel information, whether the operability of the terminal device (9) is higher than that of an operation panel part (6) (S3). When the operability of the terminal device (9) is higher than that of the operation panel part (6), the CPU (10) displays a terminal device utilization screen on a display panel (61) (S4). When the operation of an image forming device (1) by means of the terminal device (9) is selected by a user, the CPU (10) generates data for displaying an image of an operation screen on the basis of the display on the display panel (61) and a set value set by the operation of the operation panel part (6), and transmits the data to the terminal device (9) (S6).