A plurality of first multivalued images of non-defective items picked up by an image pickup device are obtained, and a plurality of characteristic amounts at least including a pixel value of a color component and edge intensities in two different directions are extracted for each pixel in the obtained first multivalued images. Selection of any one of the plurality of extracted characteristic amounts is received, and the characteristic amount of which selection is received is extracted, whereby a distribution range for determining the non-defective item is calculated. A second multivalued image of a determination target object is obtained, and the characteristic amount of which selection is received is extracted for each pixel in the obtained second multivalued image, whereby determination is made as to whether the characteristic amount is included in the distribution range corresponding to the extracted characteristic amount.