A user can visually and instinctively understand an operation to be executed, and a corresponding operation screen or input screen is easily displayed and operated. Plural flat display objects each having a predetermined displace face having each kind of information displayed in a virtual three-dimensional space are arranged in a predetermined area every category and classified into one main display object 51A and sub display objects 51B other than the display object 51A, the main display object 51A is rotated so that a display face thereof is perpendicular to or intersects to the overhead-view direction, and moved in the virtual three-dimensional space so as to be located in the overhead-view direction or in the neighborhood of the overhead-view direction while following variation of the overhead-view direction, and displayed on the display device, and the sub display objects 51B are controlled to be rotated in the virtual three-dimensional space so that display faces thereof are perpendicular to or intersect to the overhead view direction and displayed on the display screen of the display device 16.