1. A portrait illustration creation system, comprising: basic face photo data storage means for storing a plurality of pieces of face photo data of basic faces, based on which a portrait illustration is to be created, as basic face photo data; basic portrait illustration data storage means for storing a plurality of basic portrait illustrations, which are illustrations of the basic faces, as basic portrait illustration data formed of a combination of a plurality of parts; associating information storage means for storing information which associates the basic face photo data with the basic portrait illustration data; approximate basic face photo extraction means for recognizing, from face-photo-data-to-be-illustrated which is a photo of a face-to-be-illustrated of which a portrait illustration is desired to be created, the face-to-be-illustrated; performing matching between the face-to-be-illustrated and the basic faces represented by the plurality of pieces of basic face photo data stored on the basic face photo data storage means; and extracting the basic face photo data having a high approximation degree; part difference extraction means for extracting a difference on each of the parts between the basic face of the basic face photo data extracted by the approximate basic face photo extraction means and the face-to-be-illustrated represented by the face-photo-data-to-be-illustrated; part adjustment means for making an adjustment on the part having a difference of a difference amount exceeding a predetermined amount, the difference being extracted by the part difference extraction means, wherein the adjustment is made on the part of the basic portrait illustration data associated with the basic face photo data extracted by the approximate basic face photo extraction means so that the difference amount of the difference becomes equal to or less than the predetermined amount; and portrait illustration data output means for outputting basic portrait illustration data, adjusted by the part adjustment means, as portrait illustration data.