A selection device is selected from a first group in a first cluster. The node devices of the first group can communicate with a node device in a second cluster adjacent to the first cluster. The selection device performs transmission and reception of a report frame that reports an identifier of a node device included in the first group. The selection device selects from the first group a first relay device that relays a relay frame used for a communication between a node device in the first cluster and a node device in the second cluster. The first relay device determines anode device adjacent to the first relay device to be a second relay device that relays the relay frame to a node device in the second cluster.