1. An image coding device that divides each picture of a moving image signal into coding blocks each of which is a unit for predetermined coding, and carries out compression coding on each of the coding blocks by using a motion-compensated prediction, said image coding device comprising: a motion compensation unit for generating a prediction image for each of motion-compensated prediction unit areas into which said each of the coding blocks is divided by using a motion vector selected for said each of the coding blocks or said each of the motion-compensated prediction unit areas; and a variable length coding unit for variable-length-coding compressed data about a compressed difference image between an input signal corresponding to said prediction image and said prediction image, and information about said motion vector to generate a bitstream, and for multiplexing a reference image restriction flag indicating whether or not to restrict a significant reference image area which is an area on a reference image which can be used for said motion-compensated prediction to a area having a predetermined size and a predetermined shape into the bitstream, wherein said motion compensation unit determines said significant reference image area on a basis of said reference image restriction flag, and, when said prediction image includes a pixel located outside the significant reference image area, carries out a predetermined extending process.