A parent node includes: a signal reception unit receiving a parent node search signal transmitted from a child node; a RSSI measurement unit measuring a RSSI as an index indicating the intensity of wireless link with the child node transmitting the parent node search signal; a response wait time standby processing unit that, after waiting for a response wait time in accordance with the intensity of wireless link, returns a response signal to the child node as a sender of the parent node search signal; and a signal transmission unit. The child node includes: a signal transmission unit transmitting a parent node search signal; a signal reception unit receiving a response signal; and a parent node selection unit that selects a parent node for routine communication on the basis of a wait time from the transmission of a parent node search signal to the reception of a response signal.