A node device for searching for a course between start and end points in a network under constraining conditions includes a holding unit holding the constraining conditions corresponding to node devices and links connecting the node devices and indexes corresponding to the node devices and the links as network topology information; a making unit making combinations of the constraining conditions from which a part of the constraining conditions is removed; a searching unit searching for the course between the start point and the end point under the constraining conditions; a joining unit obtaining a joined result by joining the successfully searched for course to the network topology information; and a presenting unit comparing a piece of the network topology information corresponding to course information of the successfully searched for course with the removed part, extracting a nonconforming portion, and storing the joined result and the extracted nonconforming portion.