Navigation device, map displaying method and image display device

There is provided a navigation device for simultaneously displaying two screens of maps on a common display unit, the device comprising a map data storage unit for storing map data, and a resolution conversion unit for converting the resolution of the map data acquired from the map data storage unit, wherein the display unit has a predetermined display area for displaying a map based on the map data with its resolution converted. A map displaying method and an image display device are also provided.