1. An image processing apparatus for determining a non-defective item by comparing a multivalued image obtained by picking up an image of a determination target object with a multivalued image group of non-defective items, the image processing apparatus comprising: a non-defective item image acquisition device for obtaining a plurality of first multivalued images of non-defective items picked up by an image pickup device; an edge intensity calculation device for calculating edge intensities in two different directions for each pixel in the obtained first multivalued images; a mean value calculation device for calculating a mean value of the edge intensities in two different directions for each pixel in the first multivalued images, based on the calculated edge intensities; a distribution region calculation device for calculating an intercorrelation distribution region of the edge intensities in two different directions for each pixel in the first multivalued images with the calculated mean value being the center; a multivalued image acquisition device for obtaining a second multivalued image of the determination target object picked up by the image pickup device; an image edge intensity calculation device for calculating edge intensities in two different directions for each pixel in the obtained second multivalued image; and a determination device for determining whether the calculated edge intensities for each pixel in the second multivalued image are included in the calculated intercorrelation distribution region of the edge intensities for each pixel in the first multivalued images or not.