1. A video predictive encoding device comprising: a region division unit which divides an input picture into a plurality of regions; a predicted signal generation unit which determines a motion vector used to derive, from a previously-reproduced picture, a signal having a high correlation with a target region, the signal being derived as an encoding target out of the regions divided by the region division unit; a motion information storage which stores the motion vector; a residual signal generation unit which generates a residual signal between a predicted signal of the target region and a pixel signal of the target region; a residual signal compression unit which compresses the residual signal generated by the residual signal generation unit; a residual signal reconstruction unit which generates a reproduced residual signal by reconstruction from compressed data of the residual signal; an encoding unit which selects and encodes a motion vector predictor similar to a motion vector of the target region, the motion vector predictor selected from: previously-reproduced motion vectors stored in the motion information storage, side information determined from the motion vector of the target region, and the compressed data of the residual signal; and a picture storing unit which adds the predicted signal to the reproduced residual signal to reconstruct a pixel signal of the target region, and which stores the reconstructed pixel signal as the previously-reproduced picture, wherein the motion vector includes a zero-th motion vector used to generate a zero-th predicted signal, and a first motion vector used to generate a first predicted signal, wherein the predicted signal generation unit comprises: a zero-th motion information estimation unit which estimates the zero-th motion vector used to generate the zero-th predicted signal, selects, from a plurality of motion vectors stored in the motion information storage, a zero-th motion vector predictor which is similar to the estimated zero-th motion vector, and generates zero-th side information containing a zero-th motion vector predictor index to identify the selected zero-th motion vector predictor, and a motion vector difference determined from the zero-th motion vector and the zero-th motion vector predictor; a first motion information estimation unit which: selects, from a plurality of motion vectors stored in the motion information storage, a motion vector having a high correlation with the target region for generation of the first predicted signal, generates first side information containing a first motion vector predictor index to identify the selected motion vector as a first motion vector predictor, and sets the first motion vector predictor as the first motion vector; and a predicted signal combining unit which combines the zero-th predicted signal and the first predicted signal to generate the predicted signal of the target region, and further wherein the first motion information estimation unit further estimates a second motion vector for obtaining the first predicted signal, to thereby detect the second motion vector, and the first motion information estimation unit selects, from a plurality of motion vectors stored in the motion information storage, a second motion vector predictor which is similar to the estimated second motion vector and generates second side information which contains a second motion vector predictor index to identify the selected motion vector predictor and a motion vector difference determined from the second motion vector and the second motion vector predictor, wherein the predicted signal generation unit generates the first predicted signal using the first motion vector or the second motion vector, the first motion vector used when a plurality of previously-reproduced pictures are stored in a display order in the picture storage as past pictures with respect to an encoding target picture, and the second motion vector used when the plurality of previously-reproduced pictures stored in display order in the picture storage include a future picture with respect to the encoding target picture, and wherein the encoding unit encodes indication information to indicate that the first side information is encoded or the second side information is encoded, the first side information encoded in each frame or in each slice when the plurality of previously-reproduced pictures stored in display order in the picture storage are all past pictures with respect to the encoding target picture, and the second side information is encoded in each frame or in each slice when the plurality of previously-reproduced pictures stored in display order in the picture storage include the future picture with respect to the encoding target picture; and wherein the encoding unit encodes as side information of each target region, the zero-th side information, and either the first side information or the second side information based on the indication information.