1. A candidate-defect classification method, comprising the steps of: computing a feature value of a predetermined candidate defect; executing a defect classification of the candidate defect, as any one of a pattern shape defect and another type of defect, by using the computed feature value; acquiring positional information contained in a design layout data of the pattern, of a candidate defect classified as a pattern shape defect; and extracting a systematic defect from candidate defects classified as pattern shape defects, by comparing positional information contained in the design layout data of the acquired candidate defect to positional information of a portion of the sample having a high probability of having a pattern formation failure and that was obtained from the design layout data of the pattern, the systematic defect being caused by a layout shape of the pattern and/or properties of a processor for forming the pattern; wherein in the step of extracting the systematic defect, among the candidate defects classified as pattern shape defects, a candidate defect not extracted as a systematic defect in the comparison of the positional information is newly extracted as a systematic defect through an evaluation performed using a systematic defect determination criteria; wherein an image of patterns in a portion of the sample inclusive of the portion having a high probability of having a pattern formation failure and that was obtained from the design layout data of the pattern is created from the design layout data, and a pattern feature information is obtained from the created image, thereby creating a systematic defect determination criteria by using the obtained pattern feature information; and wherein the pattern feature information to be obtained includes information of an inter-pattern distance and a pattern width in the created pattern image.