a position detector configured to detect a current position of the vehicle;

a map data storage unit configured to store road map data indicating a road by links;

a route designating unit configured to designate a guidance route to a destination based on the road map data; and

a navigating unit configured to indicate an advancing direction, in which the vehicle should advance at a guidance target included in the guidance route, when the current position approaches the guidance target,

the road map data including a dummy link defined by linking a center of a rotary with an end point of a connection road link that is connected at the end point with a rotary link having an attribute associated with the rotary, and

when a rotary is the guidance target,

the navigating unit is configured to

designate (i) a first dummy link linked with a connection road link corresponding to a guidance route entering the rotary and (ii) a second dummy link linked with a connection road link corresponding to a guidance route exiting from the rotary, and

indicate an advancing direction of the vehicle at the rotary based on an angle difference between the first dummy link and the second dummy link,

the dummy link being defined with respect to a certain rotary link that is associated with a certain rotary and linked with at least one connection road link via both an entering communication link and an exiting communication link, the entering communication link being for entering the rotary link and an exiting communication link being for exiting from the rotary link, both the entering communication link and the exiting communication link having different directions from each other and from a direction of the at least one connection road link, and

with respect to the certain rotary link, a dummy link being defined by linking a center of the certain rotary with an end point of the at least one connection road link, while excluding the entering communication link and the exiting communication link of the certain rotary link.