1. An image processing device which obtains a single image by using a plurality of image-pickup elements, comprising: a plurality of image-pickup signal processing circuits that are provided for each of the image-pickup elements; an image arrangement conversion circuit which converts the read-out order of the images corresponding to the respective image-pickup elements that are output from said image-pickup signal processing circuits; image splitting means for performing image splitting on the image that is output from said image arrangement conversion circuit; image processing means for performing image processing in parallel on each of said split images; and image compression means for compressing in parallel each of the split images that are output from said image processing means, wherein said image splitting means performs image splitting with overlapping parts formed for peripheral regions of each single split image and adjacent regions that are adjacent to other split images.