To monitor the position of a moving object, such as an employee and a worker carrying a mobile information terminal, and a vehicle provided with a mobile information terminal, and to surely perform safety ensuring of the moving objects.

A radio communication network 8 is constructed by many radio slave station node groups 3, 3, etc., and a radio master station node 2 that can perform radio communication with at least one of the radio slave station node groups 3, 3, etc. A moving object monitoring computer 7 monitors the position of each moving object, and if detecting that the distance between in-vehicle mobile information terminals 41, 41, or the distance between the in-vehicle mobile information terminal 41and a portable mobile information terminal 42is within a preset separation distance L, transmits an alarm transmission signal to the in-vehicle mobile information terminals 41, 41, or the in-vehicle mobile information terminal 41and the portable mobile information terminal 42to make them sound an alarm.

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