A map data processor includes: a road map database storing a road map data having a link data with setting information of the link and road network information with connection information between links; a communication element obtaining a new link data with connection object setting information of a connection object link and coordinate information of one end of the new link from an external device; and a controller. The controller extracts a link data of a link in a predetermined geographical area with a center of the one end of the new link. The controller determines that the new link is connected to an extracted link when the connection object setting information matches the setting information of the extracted link data. The controller registers the new link data and connection information between the new link and the connection object link in the road map data.