A driver's action at a target intersection in a guided route is predicted based on driving data. When the driver is attempting to go straight ahead at a target intersection where the driver should make a turn, or when the driver is attempting to make a turn at a target intersection where the driver should go straight ahead, the predicted driver's action is determined to disagree with the guided route. In this case, an execution of an audio guidance is performed but re-execution is awaited for a predetermined period. Further, when the driver is attempting to go straight ahead at a target intersection where the driver should make a turn, an audio guidance is executed after a distance to the target intersection is determined to be smaller than a required distance computed from a vehicle speed.