1. A stereo image processing apparatus comprising: image input means for inputting, as main images, plural images constituting stereo images; encoding means for encoding stereo information for stereoscopic display control with respect to the plural main images which have been inputted by the image input means into an image; and image synthesis means for synthesizing the plural main images which have been inputted by the image input means and an encoded image which has been obtained by the encoding means in the state where corresponding areas for respective images are partitioned.