1. A defect classification method of classifying defects of a substrate based on a captured inspection object image of the substrate, comprising: a design step of setting classification classes of defects based on feature amounts of the defects and storing relations between the feature amounts of the defects and the classification classes into a storage unit; a feature amount calculation step of calculating the feature amounts of the defects of the substrate from the captured inspection object image of the substrate; and a classification step of classifying the defects of the substrate into the classification classes from the relations between the feature amounts of the defects and the classification classes stored in the storage unit based on the calculated feature amounts of the defects, said design step comprising: a first step of creating a plurality of defect templates; a second step of combining a teaching image of a substrate without defect with the defect template to create a defect model; a third step of calculating feature amounts of a defect in the defect model; a fourth step of setting a classification class of the defect with respect to the feature amounts of the defect in the defect model; and a fifth step of storing a relation between the feature amounts of the defect and the classification class into the storage unit.