Provided is a region extraction system that uses an image data analysis process, which has overcome the problem of false positives in region extraction and assists in more accurate region extraction. A luminance distribution-analyzing unit (105) is used to determine a parameter of unknown quantity for extracting a region of interest. The luminance distribution-analyzing unit (105) searches a luminance distribution management database (106) for a region, which has a luminance distribution similar to the region of interest and is easily extracted, as a similar area. The region of the similar area is extracted using a region extraction pre-processing unit (107) and the value of the parameter of unknown quantity is determined on the basis of an image feature value calculated from the region extraction results.
