PURPOSE: To provide a monitor system for detecting and tracking a missile fying on the ground level.

CONSTITUTION: A monitoring device comprises a detecting subsystem 3 and a tracking subsystem 4 mounted on a sensor satellite. The detecting subsystem 3 forms an image of the ground onto a detection focal plane 5 formed as a grid array of a pixel, through an optical system 16. And the subsystem 3 outputs the multi-spectral code from a processer 20 which detects and processes the missile from the surface gackground, when the missile exists. The tracking subsystem 4 forms the output image onto a focal plane array 94 of the pixel grid structure in the same way. The local selector image of the ground including the detected missile, is formed. Then a tracking signal processer 98 detects and tracks the missile, for monitoring the same.