PURPOSE: To correct errors in the determination of one's own ship's position at a high accuracy, by performing an image processing of digital map and data of ratio wave type navigation.
CONSTITUTION: A virtual chart radar generator section (A) receives inputs of chart images and rough one's own ship coordinates P by a radio wave type navigator or the like and a scanning is done centered on the coordinates P on the image to prepare a virtual chart radar image VC (XY) of a specified range of a coast line. A radar virtual radar image generator section A' receives inputs of an radar image and the coordinates P to prepare a radar virtual radar image VR (XY) of a coast line likewise. A 2-D correlation value of two virtual radar images thus prepared is calculated with a correlation value calculating section (B), which outputs the position maximizing the correlation value as X correction value and Y correction value. According to the correction values, the position of one's own ship is shown on a video display to perform an automatic correction continuously.