Provided is a monitoring system which can perform priority control in accordance with the wideband limitation. A priority/filter type selection processing unit (37) of a network interconnection device (11), which connects a local network (14) and a wide area network (10), selects a transmission data selection processing unit (38) on the basis of the priority level definitions of a transmission data in accordance with an event status, and a data compression method in association with the event status and the wide area network communication status, and selects and controls a filtering processing unit (33). As a consequence, the communication bandwidth in a wide area network is reduced.