1. An image encoding device for encoding an input image, comprising: a motion search section for performing motion search by using an encoding target block obtained by dividing the input image and a reference image; an adaptive PMV selection section for predicting a motion vector of the encoding target block from motion vectors of candidate blocks composed of a part or all of blocks located in the surroundings of the encoding target block, and thereby generating a prediction motion vector; and a PMV prediction encoding section for calculating a differential vector from the motion vector of the encoding block and the prediction motion vector and then performing encoding, wherein the adaptive PMV selection section includes first means of changing the number or positions of the candidate blocks to be used or alternatively setting into a zero vector the motion vector of the candidate block to be used.