An apparatus for monitoring persons within predetermined areas has a plurality of tags irremovably applicable to persons and contain data characteristic of the person. The device also comprises a signal rectifier receiving at least one signal representative of an earth leakage current, and a filter connected to the rectifier to supply a filtered rectified signal to said comparison means. The system includes at least one vehicle mounted sensor capable of sensing at least a target object and providing data related to the target object. Further on, the oscillator section outputs an oscillation signal in response to a detection signal that is outputted after a detector section compares a signal inputted therein with a predetermined signal value and detects that the inputted signal reaches a predetermined signal value. Since the silicon oxide film and the silicon nitride film exist on the conductive film of each wiring, the conductive film is not exposed at the time of etching.