1. A defect classification method to classify defects by using a classifier of instruction type on the basis of features of the defects extracted on the basis of detected signals acquired from a defect inspection apparatus, the defect classification method comprising: a priority order specification process for previously specifying target classification performance of purity and accuracy for each of defect classes, whole and in worst case, with priority order; and a classifier construction process for constructing the classifier of instruction type by setting a classify condition by means of learning using a learning algorithm and a learning parameter specified beforehand, on the basis of instruction of defect classes and feature data respectively associated therewith beforehand, wherein in the classifier construction process classification performance under the set classify condition is evaluated and whether the specified target classification performance is satisfied is displayed every item.