1. A traveling direction vector reliability determination method for determining reliability of a traveling direction vector when the traveling direction vector is calculated based on position coordinate points of a target, the position coordinate points being calculated by a radar device, the method comprising: a traveling direction vector calculation step of calculating, based on a movement history of the position coordinate points, the traveling direction vector of the target; and a reliability calculation step of calculating, in a case where the position coordinate points include at least one normally recognized coordinate point normally recognized by the radar device and at least one estimated coordinate point estimated by the radar device, the reliability of the traveling direction vector, based on at least one of information about the at least one normally recognized coordinate point and information about the at least one estimated coordinate point.