A mobile navigator comprises a distance detector for generating a running distance signal, an azimuth detector for generating a progression azimuth detecting signal, a CRT display for indicating the current position of an automotive vehicle, a microcomputer for calculating the current position of the vehicle from the distance detecting signal and the progression azimuth detecting signal and supplying the current position signal to the display, and a memory in which is stored a plurality of map data, earth's magnetic field declination information different for each area in association with the map data, and earth's magnetic field strength information.