1. A method for inspecting defects of a product having a plurality of product units formed repetitively at different locations, comprising: obtaining an image of the product units on the product having an appearance to be observed; detecting regions of the image each having an appearance which differs from an expected appearance by greater than a preset threshold; calculating feature amounts for the detected regions; classifying the detected regions into groups of defect candidates, each group including defect candidates having similar or identical appearances, or defect candidates which are disposed at corresponding identical locations or adjacent locations on the different product units and have similar or identical appearances; forming an aggregate of the feature amounts of the detected regions in the different product units, for each of the groups of defect candidates; and determining for each product unit attributes for the detected regions by comparing the feature amounts of the detected regions belonging to each group of defect candidates with a distribution of the aggregate of the feature amounts for the group of defect candidates, the attributes including a broad classification of the detected regions based on whether the detected regions belonging to each group are genuine defects.