A test packet generator of an entry device generates a delay test packet including priority information. A test packet transmitter of the entry device transmits the delay test packet to an exit device through a route corresponding to the priority information. A test packet receiver of the exit device receives the delay test packet. A reply packet transmitter of the exit device returns a reply-delay test packet toward the entry device through the same route in the counter direction. A reply packet receiver of the entry device receives the reply-delay test packet. A delay calculator of the entry device calculates a delay time on the basis of the time of transmitting the delay test packet and the time of receiving the reply-delay test packet. A route changer of the entry device changes routing appropriately on the basis of the delay time.