PURPOSE: To calculate automatically the own position of a ship and to always display its latitude and longitude by tracking automatic with respect to a reflected signal from a specified geographical point.

CONSTITUTION: A reference target selector 2 selects a reference target which is the nearest to the latitude and longitude of an initial position of the own ship fed to an initializing input 8, out of reference targets in a storage device 1, calculates the range and the azimuth to the nearest reference target from the initial position of the own ship, and sends them out to a catch controller 3. The controller 3 controls a tracking device 4 so that the tracking device 4 executes a tracking operation with respect to a reflected signal from a specified geographical point from in a video signal received from a radar device 5. The tracking device 4 calculates the range and the azimuth to the reference target, and sends them to a position operator 6. The operator 6 calculates the latitude and longitude of the own ship position based on a data from the selector 2 and supplies them to an indicator 7.