1. An image predictive encoding device comprising: circuitry configured to: divide an input image into a plurality of regions; generate a prediction signal for a target pixel signal of a target region being a processing target out of the plurality of regions resulting from the dividing; generate a residual signal between the target pixel signal and the prediction signal; and encode the residual signal, wherein: the generating of the prediction signal includes: searching a search region comprising a previously-reproduced image, for a plurality of prediction adjacent regions highly correlated to a target adjacent region consisting of a previously-reproduced adjacent pixel signal adjacent to the target region consisting of the target pixel signal; deriving at least two arbitrary combinations of prediction adjacent regions including at least one of the plurality of prediction adjacent regions obtained by the search, processing pixel signals of the prediction adjacent regions belonging to the derived combinations, by a predetermined synthesis method, the predetermined synthesis method being a weighted averaging method, thereby generating a comparison signal corresponding to the adjacent pixel signal for each of the derived combinations, and selecting a combination with a high correlation between the comparison signal and the adjacent pixel signal; and generating at least one candidate prediction signal for the target pixel signal, based on the prediction adjacent regions belonging to the selected combination, and processing the candidate prediction signal by the predetermined synthesis method, thereby generating the prediction signal; and each of the combinations of prediction adjacent regions derived in generating the prediction signal includes up to 2 n prediction adjacent regions in decreasing order of correlation to the target adjacent region, and a value of said n is an integer of not less than 2.