To obtain a navigation system where transfer is made through serial communication between a transmitting side unit including a reader and a remote receiving side unit including a buffer memory in which display can be updated well.

The navigation system comprises a first navigation unit (transmitting side unit) 10 including a reader 13 for reading out at least a map data from a map information memory medium 14 and a system controller 15, and a second navigation unit (receiving side unit) 40 including a controller 41 connected with the controller 15 through a serial communication line 30, buffer memories 42, 46 for storing a map data from the reader 13, a display image memory 43 for taking out a range required for display from the map data developed in the buffer memories 42, 46, and a display controller 44 for the map data being displayed on a display 45.