The invention provides an image processing apparatus, capable of detecting even a defect that exists in proximity to a contour line with high accuracy and determining a non-defective item with high accuracy. Edge intensities in two different directions are calculated for each pixel in the obtained first multivalued images, and a mean value of the edge intensities is calculated for each pixel in the first multivalued images. An intercorrelation distribution region of the edge intensities is calculated for each pixel in first multivalued images with the calculated mean value being the center. Edge intensities are calculated for each pixel in a second multivalued image of a determination target object, and determination is made as to 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.