Three-dimensional figures of a plurality of main spindles and tool posts of a composite lathe are displayed on a full-time display region of a display according to an arrangement of main spindles and tool posts of an actual machine. A main spindle selection state of each of the tool posts is displayed by an arrow which is seen to move toward the main spindle figure from each of the tool post figures. It is possible to provide a display device which can viscerally understand an operating state of the machine and is excellent in design, and it is possible to easily instruct a controller a setting and a command which affects the machine state.