To provide the network system which can easily perform efficient maintenance by sending an agent program.

A communication network 10 includes network sites 12 and service terminal machines 16 and 18, a maintenance terminal machine 20 or a server 22 can be connected to each of the sites. The service terminal machines 16 and 18 may be ATMs or point-of-sales(POS) terminal machines and have at least one service element 44 like a card conveying machine or coin container which should be held in an operation state. An intelligent agent program 50 moves among the terminal machines 16, 18 and 20 while gathering information from the terminal machines 16, 18 and 20 that it visits or distributing information thereto. The gathered or distributed information is used to facilitate the efficient maintenance of the service terminal machines 16 and 18.