An operation device, comprising: a preview image displaying unit configured to display plural setting item keys and icons corresponding to setting items in a predetermined screen, display a preview image that resembles a printed matter in the predetermined screen, switch and display a setting value input screen that displays setting value keys for selecting respective plural setting values for a setting item corresponding to one of the plural setting item keys when the setting item key is pressed down in the predetermined screen, change a preview image displayed in the setting value input screen to a preview image corresponding to a setting value that corresponds to one of the setting value keys when the setting value key is pressed down and change a setting value of the setting item to the setting value of the pressed-down setting value key, switch and display the predetermined screen and change the preview image displayed in the predetermined screen to a preview image corresponding to the changed setting value when a confirmation key is pressed down in the setting value input screen; characterized by an obtaining unit configured to obtain setting values of either a setting item key among the setting item keys or an icon among the icons one by one when a user performs a predetermined operation to the setting item key or the icon without pressing-down the setting item keys while the predetermined screen is displayed; and a generating unit configured to generate preview images corresponding to respective ones of the obtained setting values; wherein the preview image displaying unit is further configured to switch and display the generated preview images in the predetermined screen in turn with a predetermined time interval; and the preview image displaying unit is further configured to switch and display the preview images displayed in the predetermined screen so as to enable the preview images to be pressed down and change a setting value of the setting item corresponding to the icon to the setting value corresponding to a preview image among the preview images when a user presses down the preview image image in the predetermined screen without switching and displaying the setting value on the setting value input screen. a preview image displaying unit configured to display plural setting item keys and icons corresponding to setting items in a predetermined screen, display a preview image that resembles a printed matter in the predetermined screen, switch and display a setting value input screen that displays setting value keys for selecting respective plural setting values for a setting item corresponding to one of the plural setting item keys when the setting item key is pressed down in the predetermined screen, change a preview image displayed in the setting value input screen to a preview image corresponding to a setting value that corresponds to one of the setting value keys when the setting value key is pressed down and change a setting value of the setting item to the setting value of the pressed-down setting value key, switch and display the predetermined screen and change the preview image displayed in the predetermined screen to a preview image corresponding to the changed setting value when a confirmation key is pressed down in the setting value input screen; change a setting value of the setting item to the setting value of the pressed-down setting value key, switch and display the predetermined screen and change the preview image displayed in the predetermined screen to a preview image corresponding to the changed setting value when a confirmation key is pressed down in the setting value input screen; an obtaining unit configured to obtain setting values of either a setting item key among the setting item keys or an icon among the icons one by one when a user performs a predetermined operation to the setting item key or the icon without pressing-down the setting item keys while the predetermined screen is displayed; and a generating unit configured to generate preview images corresponding to respective ones of the obtained setting values;