1. A video predictive decoding method executed by a video predictive decoding device, comprising: a decoding step of decoding a compressed data out of plural sets of compressed data obtained by encoding a plurality of divided regions, the compressed data comprising side information and a residual signal of a target region, which is a target to be decoded; a motion information reconstruction step of reconstructing a motion vector used to generate a predicted signal of the target region from the side information; a motion information storing step of storing the motion vector in a motion information storing unit; a motion compensation step of generating the predicted signal of the target region, based on the motion vector; a residual signal reconstruction step of reconstructing a reproduced residual signal of the target region from the compressed data comprising the residual signal; and a picture storing step of adding the predicted signal to the reproduced residual signal to reconstruct a pixel signal of the target region, and storing the reconstructed pixel signal as a previously-reproduced picture, wherein in the decoding step, the video predictive decoding device decodes zero-th side information and first side information, wherein the zero-th side information contains a zero-th motion vector difference, and a zero-th motion vector predictor index used to identify, as a zero-th motion vector predictor, one motion vector selected from a plurality of motion vectors stored in the motion information storing step, wherein the first side information contains a first motion vector predictor index used to identify as a first motion vector predictor one motion vector selected from a plurality of motion vectors stored in the motion information storing step, wherein the motion information reconstruction step comprises: a zero-th motion information reconstruction step of generating the zero-th motion vector predictor based on the zero-th motion vector predictor index, and adding the generated zero-th motion vector predictor to the zero-th motion vector difference to reconstruct a zero-th motion vector; and a first motion information reconstruction step of generating the first motion vector predictor based on the first motion vector predictor index, to reconstruct the generated first motion vector predictor as a first motion vector, wherein in the motion compensation step, the video predictive decoding device combines two signals derived from the previously-reproduced picture, based on the zero-th motion vector and the first motion vector, to generate the predicted signal of the target region, wherein in the decoding step, the video predictive decoding device further decoding, in each frame or in each slice, indication information to indicate whether the first side information contains a motion vector difference, wherein when the indication information indicates that the first side information contains a first motion vector difference, the video predictive decoding device decoding the motion vector difference as the first side information, and wherein in the first motion information reconstruction step, when the indication information indicates that the first side information does not contain the first motion vector difference, the video predictive decoding device generating the first motion vector predictor, based on the first motion vector predictor index, and reconstructing the generated first motion vector predictor as the first motion vector, and wherein in the first motion information reconstruction step, when the indication information indicates that the first side information contains the first motion vector difference, the video predictive decoding device generating the first motion vector predictor, based on the first motion vector predictor index, and adding the generated first motion vector predictor to the decoded motion vector difference to reconstruct the first motion vector, wherein the zero-th side information further contains a reference frame index to identify a reference frame for generating a zero-th predicted signal, wherein the first side information further contains a reference frame index to identify a reference frame for generating a first predicted signal, wherein in the motion information storing step, the video predictive decoding device further stores the reference frame index to identify the reference frame for generating the zero-th predicted signal and the reference frame index to identify the reference frame for generating the first predicted signal, in motion information storing unit, wherein the zero-th motion vector predictor index identifies, out of a plurality of reference frame indices stored in the motion information storing unit, a zero-th reference frame predictor index as well as the zero-th motion vector predictor, wherein the first motion vector predictor index identifies, out of a plurality of reference frame indices stored in the motion information storing unit, a first reference frame predictor index as well as the first motion vector predictor, wherein in the zero-th motion information reconstruction step, the video predictive decoding device generates, on a further basis of the reference frame index contained in the zero-th side information and the zero-th reference frame predictor index, the zero-th motion vector predictor by using a motion vector selected from a plurality of motion vectors stored in the motion information storing unit based on the zero-th motion vector predictor index, and wherein in the first motion information reconstruction step, the video predictive decoding device generates, on a further basis of the reference frame index contained in the first side information and the first reference frame predictor index, the first motion vector predictor by using a motion vector selected from a plurality of motion vectors stored in the motion information storing unit based on the first motion vector predictor index.