1. A route searching method for execution by a computer for finding a recommended route from a departure place to a destination, wherein the computer stores preference parameters calculated as road usage frequencies, representing preference degrees, according to preference items which can be factors for route selection, and wherein the computer executes the steps of: receiving location information specifying a departure place and a destination; selecting, out of the preference parameters, at least one preference parameter similar to user attribute data; adjusting, based on the selected preference parameter, a cost of each road link; and determining, based on the adjusted cost of each road link, a minimum-cost route from a departure place to a destination.