A CPU 411 splits selected image data GD into a plurality of areas (pixel data groups), analyzing the image data GD in terms of area units, and determining the color range of the areas of the image data GD. The CPU 411 determines color range areas by associating adjacent areas of the same color range when determining the color range for the areas of the image data GD. The CPU 411 acquires position data for the color range areas that have been determined. The CPU 411 acquires position conditions (main object conditions) from ROM/HDD 413, and narrows the main object candidates to “sky, green, or people.” The CPU 411 finally determines the main object by comparing the position data of the color range color areas and the position conditions corresponding to the narrowed main object.