1. A navigation system, comprising: a navigation apparatus configured to carry out guidance by outputting a voice message; a location and speed detector, configured to detect a location and a speed of the navigation apparatus; a voice message weight storage, configured to store voice message weight association information, which associates a weight with each of multiple voice messages; a rule storage, configured to store priority rule information denoting a rule for deciding a priority for each of the multiple voice messages; a priority decision module, configured to decide a priority for each of the multiple voice messages based on the priority rule information; a voice output, configured to output the multiple voice messages from the navigation apparatus in a sequence conforming to the decided priority, a server configured to communicate with the navigation apparatus, the server including a reference driving performance information transmitter configured to send reference driving performance information to the navigation apparatus, wherein the reference driving performance information is driving performance characteristics information constituting a reference; the navigation apparatus includes: a characteristics acquisition receiver configured to acquire driving performance characteristics of a driver, who drives a vehicle including the navigation apparatus; and an evaluation score calculator configured to calculate an evaluation score of the driver based on the reference driving performance information and the driving performance characteristics of the driver; wherein a rule denoted by the priority rule information is a rule for deciding a priority for each voice message based on: the detected location and speed of the navigation apparatus, the weight of each of the voice messages denoted by the voice message weight association information, and the evaluation score of the driver.