To reduce a load required for data transfer and data processing to improve processing speed of those. A display data memory stores as display data a configuration image simulating an overall configuration of a combination of a main body and an attachment. An image display device provided on either one of the main body and the attachment includes a display screen having a display area divided into a plurality of divisional areas for displaying the configuration image. A CPU determines displaying and non-displaying on each of the plurality of divisional areas, and controls the image display device to allow a part of the configuration image to be displayed on a divisional area which is determined to be displayed in accordance with display data, and to allow an other part of the configuration image not to be displayed to on a divisional area which is determined not to be displayed.