To prevent a band used for communication data from decreasing by suppressing an increase in traffic although speedily detecting change of network topology.

In the multi-hop communication network composed of a plurality of nodes N, a communication means 11 transmits a hello message at proper time, and finds and registers link costs for direct communication with an adjacent node N in an adjacent node table Tb1. A route for transmitting communication data is selected using link costs registered in adjacent node tables Tb1 of respective nodes N. A signal processing means 10 transmits a first hello message at first time intervals in a normal mode, but selects a transition mode wherein a second hello message is transmitted at shorter time intervals than in the normal mode right after the power source is turned ON. A node N in the normal mode which has received the second hello mode transmits the first hello message at the shorter time intervals than in the normal mode.