an entrance lane number determining unit that determines that an entrance road entering a guidance intersection includes one or more lanes accessible to an exit road exiting from the guidance intersection, the entrance road and the exit road being along a guidance route;

an exit lane number determining unit that determines that the exit road includes more than one lane when the entrance lane number determining unit determines that the entrance road includes only one lane accessible to the exit road;

a branching point determining unit that determines that a branching point is present along the guidance route within a given distance after the guidance intersection when the exit lane number determining unit determines that the exit road includes more than one lane;

a deviation determining unit that determines, when the branching point determining unit determines that the branching point is present within the given distance, that approaching the branching point by using a natural exit lane of the exit road, the natural exit lane exiting naturally from the guidance intersection, will result in entering a road that is not included in the guidance route; and

a lane-change guiding unit that suggests before entering the guidance intersection that a lane change be required from the natural exit lane to another exit road lane after passing through the guidance intersection, based on a result determined by the deviation determining unit.