To efficiently shoot down a plurality of targets with missiles by parallel-displacing the moving direction vector of a centroid point detected from picture signals.

An infrared image sensor 1 detects infrared rays radiated from a target and outputs picture signals 2 and binarizing means 3 binarizes the picture signals 2 and outputs the binarized signals as binarized picture signals 4. A direction vector detecting means 14 calculates the moving direction of the centroid point of the whole picture and outputs the direction as a direction vector 15. A direction vector shifting means 16 gradually parallel-displaces the vector 15 from both ends and outputs the displaced vector 15 as an area numbering direction vector 17. A cross detecting means 18 arranges the numbers of the areas of the vector 17 crossed by the vector 17 associating with parallel displacement and outputs the numbers as the rearranged numbers 19 of the areas. A position coordinate selecting means 23 selects the position coordinates corresponding to the number 22 of the area corresponding to a locked-on target and outputs the coordinates as the position coordinates of the target.