To solve the problem that displaying of a detailed map requires much time in a navigation system displaying every time downloading the data of a detailed map having a lot of quantities of information in a navigation system.

Displaying of not only the detailed map but also a simple map, having a small quantities of information, is made possible to be selectively displayed, and data of the displayable range of more is previously downloaded to be stored for the detailed map data. When the displaying is needed in this range, the stored detailed map data are displayed by dividing the data to read it. On the other hand, when the displaying of the simple map is selected, additional data are downloaded during this reading and displaying, the detailed map data are completed to be stored, and then the subsequent displaying of the detailed map is prepared. Consequently, the times needed for the diversification of map indication and for the displaying of the detailed map is shortened.