Network system

The present invention improves reliability of communication in a network in which a plurality of apparatuses is classified into a plurality of hierarchy levels, in a case where communication irrelevant to the hierarchy levels and communication within each of the hierarchy levels are performed using physical wiring. A physical first wiring (501) is connected to a first indoor unit (121) and an outdoor unit (110) which are first level apparatuses. A physical second wiring (502) is connected to a second indoor unit (122) which is a second level apparatus. A first intermediate unit (150), which is a first intermediate apparatus, has a first filter (151) which is constantly connected to the first wiring (501) and the second wiring (502). The first intermediate unit (150) communicates with the outdoor unit (110) and the second indoor unit (122) by using a first signal. The first filter (151) is disposed so as to facilitate passage therethrough of a high-frequency first signal to be used for communication among the outdoor unit (110), the first indoor unit (121), the first intermediate unit (150), and the second indoor unit (122), and so as to retard passage therethrough of a low-frequency second signal to be used for communication between the first intermediate unit 150 and the second indoor unit 122.