1. An image region extracting apparatus that extracts a target region from an image based on a designation region, the apparatus comprising: a spatial change learning section that acquires a pixel value change pattern and a distance change pattern of each part of the image, the pixel value change pattern being a spatial change characteristic of a pixel value component, and the distance change pattern being a spatial change characteristic of a distance component from a reference position to a subject; and a region dividing section that extracts the target region based on similarities of the pixel value change pattern and the distance change pattern between the designation region and each part of the image.