Abstract: A vehicle-mounted display device includes an input unit, a foreground image acquisition unit, a brightness value calculation unit, a background image conversion unit, a combining unit, and a display unit. The foreground image acquisition unit acquires a foreground image including vehicle information. The brightness value calculation unit calculates a brightness value of a background image input from the input unit. The background image conversion unit converts the background image input from the input unit in accordance with the brightness value of the background image and color information of a theme color. The combining unit combines the foreground image and the background image converted by the background image conversion unit, and the display unit displays an image combined by the combining unit.