1. A road map data learning device comprising: a new road detection unit configured to detect a new road based on a travel locus of a vehicle and road map data, the new road being not included in the road map data; a road learning unit configured to perform learning of a new road detected by the new road detection unit as a learned road being functional additionally to the road map data; a learned road deleting unit configured to delete the learned road according to an operation of a user; a storage device configured to store learning-prohibited pattern information; and a deleted road storage processing unit configured to store a feature of a learned road, which is deleted by the learned road deleting unit, as the learning-prohibited pattern information, wherein the road learning unit is further configured to restrict the learning of a new road detected by the new road detection unit when a feature of the new road coincides with the learning-prohibited pattern information stored in the storage device.