To solve a matter that it is difficult for a user to identify an apparatus easily when a plurality of apparatus of the same model number are connected with a network.

The network apparatus controller 101 detects variation in operating state occurring in an AV apparatus when a user operates a desired AV apparatus, and stores the address of an AV apparatus in which variation in operating state is detected as control information Tctr. An apparatus operating information acquisition control unit 203 transmits state confirmation commands Cst2-Cstn to the AV apparatus 102-104, respectively. Subsequently, the apparatus operating information acquisition control unit 203 receives response commands Cres2-Cresn replied in response to the state confirmation commands Cst2-Cstn from a command transmitter 202, and determines whether each of the AV apparatus 102-104 is in power on state or power off state based on information included in a received response command Cres2-Cresn.