PURPOSE: To prevent previously the collision of ships and others and thus to ensure safety of the sailing, by dividing the radar scanning region into pural numbers of regions which are enclosed by the lines showing two distances plus directions angle line and the scanning these regions in sequence.

CONSTITUTION: The gate is produced synchronizing with the transmission pulse. And width of the R-directin gate is set to the time when the electric wave propagates R2-R1, and the Az-direction gate is set to the transmission pulse time equivalent to the azimuth of OWAz1 and Az2W2π for one scan. Thus, the first scan extracts only the target of region 11. The Az-direction gate is similar to the first scan at and after the second scan, but the R-direction gate is shifted from the upper inside of the rader screen to the outside through regions 12W16 and thus delayed by the time when the electric wave propagates the R-direction gate width of inner side by one. In this way, the extraction becomes possible for regions 12W16. Furthermore, the shift is given from inside to outside of the region, and the target is registered from the place closer to the own ship. Thus, the gangerous ships near the own ship can be caught assuredly.