A navigation system has a navigation apparatus mounted on a vehicle, and a computer apparatus which is connected with the navigation apparatus to enable to communicates with the navigation apparatus. When the navigation apparatus receives route search information including recommended-route information from the computer apparatus, the navigation apparatus transmits a notice of completion of reception to the computer apparatus, generates traveling route information of the vehicle which moves on the basis of the route search information, and transmits guidance result information to the computer apparatus. The computer apparatus transmits recommended-route information which is generated on the basis of a predetermined algorithm, to the navigation apparatus, receives from the navigation apparatus the reception completion notice and the guidance result information including the traveling route information of the vehicle, and modifies the algorithm on the basis of the recommended-route information and the traveling route information.