PURPOSE: To provide a road map data input device with which the direction data of one-way traffic can be easily inputted and input errors can be reduced.

CONSTITUTION: In the state of displaying links 10a-10e through the nodes of node numbers 1001, 1004, 1002 and 1003, an operator successively selects the links from the link 10b on the starting side of one-way traffic to the link 10d on the terminal side of one-way traffic. A processor recognizes the direction of one-way traffic from the input order of links and sets direction data 20a and 20c in a forward direction concerning the link, in which the node number on the starting side of one-way traffic is smaller than the node number on the terminal side, and sets direction data 20b in a backward direction when the node number on the starting side is larger than that on the terminal side.