PURPOSE: To notice a monitor screen by a monitor personnel, by giving an alarm, only when a mobile body exists within a range to be noticed in the monitor screen.

CONSTITUTION: An ITV camera 1 is fixed and picks up a specified range, and its picture is reproduced on a monitor television 2 at all times. A screen analyzer 3 stores signals from the ITV camera 1 for a prescribed time and gives an output to driven an alarm 4 when a mobile body exists within the range of left side picture sectioned with A-B line. The data analysis like this can be performed with the pattern recognizing technique consisting of a CPU, a data storage memory and a data processing memory. The pattern screen stored in the preceding time and that received this time are compared and an alarm instruction is given when they are discident.