There is provided a display device which can make the user understand a motion of a control target device without preparing a three-dimensional model faithfully reproducing an outer view of each control target device. A PC (10) as the display device presents options of a virtual mechanism, and accepts a selection thereof. The virtual mechanism has a structure in which a plurality of mechanism elements are combined having interlocking relationships, and includes an abstracted mode not imitating a mode of a specific control target device. The options of the virtual mechanism include a plurality of virtual mechanisms which are mutually different in kind of the mechanism element or in form of the interlocking relationship among the mechanism elements. Using command values or actual measured values of a sequence of positions as execution results of a control program, the PC (10) displays on a screen a moving image showing a state of the selected virtual mechanism in every period when the command value is inputted into the control target device or in a specified period among the periods.