1. A defect inspection apparatus for inspecting whether or not a product has defects, comprising: a manufacturing desirable image forming circuit for forming a manufacturing desirable image from an original image, the original image being formed for manufacturing the product, the manufacturing desirable image being an modified image of the original image which is suitable to be compared with an image of the product for inspection; an inspection portion setting circuit for setting an inspection portion, where a defect may occur due to a manufacturing process of the product, within the manufacturing desirable image; a pattern superimposing circuit for superimposing a defect pattern on the inspection portion of the manufacturing desirable image so as to form a template image including the defect pattern; a photographing circuit for photographing the product to obtain the image of the product; a template matching circuit for comparing the image of the product with the template image including the defect pattern; and a defect present/absent judging circuit for judging whether or not the defect is present based upon an evaluation value outputted from the template matching circuit.