An image decoding apparatus has a video data decoder for receiving and decoding encoded video data to acquire a plurality of reconstructed images; a subsidiary data decoder for receiving and decoding subsidiary data to acquire subsidiary motion information; and a resolution enhancer for generating motion vectors representing time-space correspondences between the plurality of reconstructed images, based on the subsidiary motion information acquired by the subsidiary data decoder, and for generating a high-resolution image with a spatial resolution higher than that of the plurality of reconstructed images, using the generated motion vectors and the plurality of reconstructed images acquired by the video data decoder.