A navigation device capable of communicating with an in-vehicle device installed in a vehicle, comprising: a deviated point information acquiring unit ( 91, S101) that is configured to acquire deviated point information regarding a deviated point where a vehicle traveling a set route has deviated the set route; a post-deviation travel history information acquiring unit ( 91, S109) that is configured to acquire post-deviation travel history information regarding a travel history indicating a route that past deviated vehicles have traveled after having deviated the set route at the deviated point, each deviated vehicle being the vehicle traveling the set route and having deviated the set route at the deviated point; a travel determining unit ( 91, S110) that is configured to determine based on the post-deviation travel history information for each past deviated vehicle whether each deviated vehicle has traveled along a reroute set after deviating the set route at the deviated point; a reroute travel rate judging unit ( 91, S111) that is configured to judge whether a rate of the deviated vehicles which were determined as having traveled along the reroute among the deviated vehicles is a first predetermined value or more; a guidance determining unit (91, S112) that is configured to, if the reroute travel rate judging unit has judged that the rate of the deviated vehicles which were determined as having traveled along the reroute is the first predetermined value or more, determine that guidance regarding the set route at the deviated point is not appropriate; and a changing unit ( 91, S113) that is configured to, if the guidance determining unit ( 91, S112) has determined that the guidance regarding the set route at the deviated point is not appropriate, changes the guidance regarding the set route at the deviated point. a deviated point information acquiring unit ( 91, S101) that is configured to acquire deviated point information regarding a deviated point where a vehicle traveling a set route has deviated the set route; a post-deviation travel history information acquiring unit ( 91, S109) that is configured to acquire post-deviation travel history information regarding a travel history indicating a route that past deviated vehicles have traveled after having deviated the set route at the deviated point, each deviated vehicle being the vehicle traveling the set route and having deviated the set route at the deviated point; a travel determining unit ( 91, S110) that is configured to determine based on the post-deviation travel history information for each past deviated vehicle whether each deviated vehicle has traveled along a reroute set after deviating the set route at the deviated point; a reroute travel rate judging unit ( 91, S111) that is configured to judge whether a rate of the deviated vehicles which were determined as having traveled along the reroute among the deviated vehicles is a first predetermined value or more; a guidance determining unit (91, S112) that is configured to, if the reroute travel rate judging unit has judged that the rate of the deviated vehicles which were determined as having traveled along the reroute is the first predetermined value or more, determine that guidance regarding the set route at the deviated point is not appropriate; and a changing unit ( 91, S113) that is configured to, if the guidance determining unit ( 91, S112) has determined that the guidance regarding the set route at the deviated point is not appropriate, changes the guidance regarding the set route at the deviated point.