In order to promote the use of a display panel as an operation panel part, if a communicable terminal device (9) is detected (S1), a CPU (10) requests the terminal device (9) to transmit panel information (S2), and determines, on the basis of the panel information, whether or not the operability of the terminal device (9) is higher than that of an operation panel part (6) (S3). If 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). If an operation of an image forming device (1) by the terminal device (9) is selected by a user, the CPU (10) generates data for displaying an image of an operation screen based on the display on the display panel (61) and a setting value set by the operation of the operation panel part (6), and transmits the data to the terminal device (9) (S6).