A route search device comprising: a basic congestion information acquisition unit adapted to acquire basic congestion information from an information serving center, the basic congestion information being congestion information of specific links, the basic congestion information not comprising center traffic information obtainable from a center, the center traffic information being congestion information of links other than the specific links; a destination setting unit adapted to set a destination; a first route search unit adapted to search for a route from a departure point to the destination set by the destination setting unit using the basic congestion information acquired by the basic congestion information acquisition unit and to determine a first travel route based on a searched result; an information judgment unit adapted to judge based on the first travel route determined by the first route search unit whether the center traffic information is necessary to be acquired from the center; an additional congestion information acquisition unit adapted to, if the information judgment unit has judged that the center traffic information is necessary to be acquired from the center, acquire the center traffic information from the center; a second route search unit adapted to search for a route from the departure point to the destination set by the destination setting unit using the center traffic information acquired by the additional congestion information acquisition unit and a link judgment unit adapted to judge whether the first travel route includes one or more links other than the specific links for which the basic congestion information were acquired, wherein the information judgment unit, if the link judgment unit has judged that the first travel route does not include the one or more links other than the specific links, is adapted to judge that the center traffic information is not necessary to be acquired from the center; characterized by a third route search unit, if the link judgment unit has judged that the first travel route includes the one or more links other than the specific links, adapted to search for a route from the departure point to the destination set by the destination setting unit under the assumption that the one or more links other than the specific links are congested and to determine a third travel route based on a searched result; and a route matching judgment unit adapted to judge whether the first travel route matches with the third travel route, wherein the information judgment unit, if the route matching judgment unit has judged that the first travel route does not match with the third travel route, is adapted to judge that the center traffic information is necessary to be acquired from the center. a basic congestion information acquisition unit adapted to acquire basic congestion information from an information serving center, the basic congestion information being congestion information of specific links, the basic congestion information not comprising center traffic information obtainable from a center, the center traffic information being congestion information of links other than the specific links; a destination setting unit adapted to set a destination; a first route search unit adapted to search for a route from a departure point to the destination set by the destination setting unit using the basic congestion information acquired by the basic congestion information acquisition unit and to determine a first travel route based on a searched result; an information judgment unit adapted to judge based on the first travel route determined by the first route search unit whether the center traffic information is necessary to be acquired from the center; an additional congestion information acquisition unit adapted to, if the information judgment unit has judged that the center traffic information is necessary to be acquired from the center, acquire the center traffic information from the center; a second route search unit adapted to search for a route from the departure point to the destination set by the destination setting unit using the center traffic information acquired by the additional congestion information acquisition unit and a link judgment unit adapted to judge whether the first travel route includes one or more links other than the specific links for which the basic congestion information were acquired, wherein the information judgment unit, if the link judgment unit has judged that the first travel route does not include the one or more links other than the specific links, is adapted to judge that the center traffic information is not necessary to be acquired from the center; characterized by a third route search unit, if the link judgment unit has judged that the first travel route includes the one or more links other than the specific links, adapted to search for a route from the departure point to the destination set by the destination setting unit under the assumption that the one or more links other than the specific links are congested and to determine a third travel route based on a searched result; and a route matching judgment unit adapted to judge whether the first travel route matches with the third travel route, wherein the information judgment unit, if the route matching judgment unit has judged that the first travel route does not match with the third travel route, is adapted to judge that the center traffic information is necessary to be acquired from the center.