1. A concealed regions complementing system of free viewpoint video images in which when the free viewpoint video images are output, the pixels in background regions concealed by foreground regions in a reference video image are complemented, said system comprising background regions extracting means for extracting, from an input video image, the background regions as a single-layered background video image and multi-layered background video images divided in accordance with depth, a single-layered background buffer for storing the single-layered background video image, and multi-layered background buffers for storing the multi-layered background video images, wherein when the free viewpoint video images are output, the pixels in the background regions concealed by foreground regions in a reference video image are complemented using the pixels of the multi-layered background video images stored in the multi-layered background buffers, and the pixels which are not complemented by this operation are complemented using the pixels of the single-layered background video image stored in the single-layered background buffer.