1. An image predictive decoding method comprising: a data analysis step of extracting with a processor, from compressed data of an image, encoded data of prediction information to indicate a prediction method to be used in prediction of a signal of a target region serving as a decoding target, encoded data of a predicted signal of the target region, and encoded data of a residual signal, wherein the compressed data of the image is a result of partition into a plurality of regions and encoding of the target region; a prediction information decoding step of decoding the encoded data of the prediction information with the processor to restore a prediction block partitioning type and motion information, the prediction block partitioning type indicating a number of prediction regions and region shapes of the prediction regions, wherein the prediction regions are sub-partitioned regions of the target region, and the motion information is used for acquisition of each of a plurality of predicted signals of the respective prediction regions from a previously-reconstructed signal; a predicted signal generation step of generating the predicted signal of the target region with the processor based on the prediction information associated with the target region; a residual signal restoration step of restoring with the processor a reconstructed residual signal of the target region from the encoded data of the residual signal; and a recording step of the processor adding the predicted signal to the reconstructed residual signal to restore a pixel signal of the target region, and storing the pixel signal as the previously-reconstructed signal, wherein the prediction information decoding step further comprises the steps of: decoding with the processor the prediction block partitioning type of the target region and storing the prediction block partitioning type as previously-decoded prediction information into a prediction information storage that stores previously-decoded prediction information; selecting a candidate for motion information with the processor to be used in generation of a predicted signal of a target prediction region serving as a next prediction region based on: the prediction information of a region neighboring the target region, a number of previously-decoded prediction regions in the target region, and the previously-decoded prediction information of the target region, wherein, when the prediction block partitioning type indicates that the target region is horizontally partitioned into a first prediction region on the upper side and a second prediction region on the lower side, and the target prediction region serving as the next prediction region is the second prediction region, the candidate for motion information is selected from previously-decoded motion information of a region neighboring the target prediction region and excluding the first prediction region; decoding with the processor, according to a number of candidates for motion information selected, merging block information using the selected candidate for motion information and the motion information, or decoding with the processor either one of the merging block information or the motion information, wherein the merging block information is indicative of generation of the predicted signal of the target prediction region; and storing the motion information to be used in generation of the predicted signal of the target prediction region into the prediction information storage.