ROUTE SEARCHING SYSTEM, ROUTE SEARCHING METHOD, NAVIGATION SYSTEM AND COMPUTER PROGRAM PRODUCT

A route searching system is provided with: a road map database for storing a road map data; a searching device for performing a link cost calculation on the basis of the road map data and thereby searching an optimal route. The searching device increases or decreases the link cost of a link corresponding to a road section that requires a difficult turn on a route option, the difficult turn being a right turn or a left turn, one of which is more difficult than the other in accordance with a traffic rule, and connecting a node corresponding to an intersection, in at least two cases depending on the difficulty of the difficult turn at the intersection.