To immediately detect a state wherein a route through which nodes transmit communication data to each other becomes unusable, and to disallow the detected route to be selected in next route selection.

In the multi-hop communication network composed of a plurality of nodes N, a communication quality acquisition means 12 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. When the communication data are transmitted using the selected route, an evaluated value correcting means 15 increases the link costs between a transmission-destination node N and node in the adjacent node table Tb1 of the transmission-destination node N on condition that the node N on the route does not receive an acknowledge from the transmission-destination node N after transmitting the communication data to the adjacent node.