To provide a terminal monitoring system and terminal monitoring device capable of ensuring high precision and sufficient reliability without using a precise or expensive portable device.

This terminal monitoring system 10 has a terminal device to be monitored 200, a terminal monitoring device 100, and an information communicating terminal device 300 having an input part 312, a display part 311, and a receiving part 320. The terminal monitoring device has a terminal position management device 110; a position error information management device 140; a monitoring range specifying management device 130 having an image information processing part 134 for visually displaying a combination of geographic information and position error information based on the input from the input part and a monitoring range forming part 135; a monitoring range information management device 120 having monitoring range information management parts 122 and 123 and a monitoring range determination part 124 for determining whether the terminal device to be monitored is located within the monitoring range or not; and a report transmitting means 129 for reporting the determination result.