Route search device, route search method, and correponding computer programm

Basic congestion information is acquired from a VICS center 5; first route search processing searching for a route to a destination based on the acquired basic congestion information is executed; it is judged based on a first travel route determined by the first route search processing whether center traffic information is necessary to be acquired from a probe center 4; if it is judged that the center traffic information is not necessary to be acquired, the first travel route is set as a guidance route; if it is judged that the center traffic information is necessary to be acquired, additional congestion information is acquired from the probe center 4 as the center traffic information, second route search processing that searches for a route based on the acquired additional congestion information is executed; and a second travel route determined by the second route search processing is set as the guidance route.