1. An image area extract unit for extracting a characteristic portion from an original image, comprising: original image acquisition means for acquiring said original image; training image acquisition means for acquiring a training image taken under a same condition under which said original image is taken; supervisory image acquisition means for acquiring a supervisory image that designates a characteristic portion of said training image, said supervisory image including pixels each of which provides a supervisory output, the characteristic portion of said training image corresponding to the characteristic portion of said original image; model generation means for generating a pixel evaluation model based on a relationship between a value of a first pixel of said training image and the supervisory output provided by a second pixel of said supervisory image, said second pixel corresponding to said first pixel, said pixel evaluation model receiving a value of one of pixels of said original image as an input and outputting a feature value of the pixel; and area definition means for calculating the feature value of each pixel of said original image by using said pixel evaluation model and defining an extractive area of said original image based on the feature value of each pixel of said original image, said extractive area including the characteristic portion of said original image.