An image predictive decoder comprising a memory that stores a program executable by the image predictive decoder to: extract, from compressed data in which an image is divided into a plurality of regions and encoded, encoded data of identification information that specifies an identification of a region width of a first partition of the target region that is not agreed upon to use in advance between an image predictive encoder and the image predictive decoder and is used to produce a prediction signal of a target region, and encoded data of a residual signal; read out the identification specified in the identification information; prepare a list that consists of entries corresponding, respectively, to a plurality of neighbouring regions that neighbour the target region; select a neighbouring region from the list, the selected neighbouring region being identified by the identification specified in the identification information; produce the prediction signal of the target region by using prediction information for the specified neighbouring region comprising (i) mode information that specifies an inter-picture prediction method, (ii) a reference picture number, and (iii) a motion vector, all of which are used for prediction of the specified neighbouring region; restore a reproduction residual signal of the target region from the encoded data of the residual signal; produce a reproduction signal of the target region based on the prediction signal of the target region and the reproduction residual signal; and store the reproduction signal of the target region as the reconstructed signal in the memory; wherein the memory further stores a program executable by the image predictive decoder to: decode the encoded data of the identification information to restore the identification information; determine whether the target region is divided into the first partition and a second partition; and when the target region is divided into the first partition and the second partition, produce a prediction signal of the first partition of the target region by using the prediction information for the specified neighbouring region. extract, from compressed data in which an image is divided into a plurality of regions and encoded, encoded data of identification information that specifies an identification of a region width of a first partition of the target region that is not agreed upon to use in advance between an image predictive encoder and the image predictive decoder and is used to produce a prediction signal of a target region, and encoded data of a residual signal; read out the identification specified in the identification information; prepare a list that consists of entries corresponding, respectively, to a plurality of neighbouring regions that neighbour the target region; select a neighbouring region from the list, the selected neighbouring region being identified by the identification specified in the identification information; produce the prediction signal of the target region by using prediction information for the specified neighbouring region comprising (i) mode information that specifies an inter-picture prediction method, (ii) a reference picture number, and (iii) a motion vector, all of which are used for prediction of the specified neighbouring region; restore a reproduction residual signal of the target region from the encoded data of the residual signal; produce a reproduction signal of the target region based on the prediction signal of the target region and the reproduction residual signal; and store the reproduction signal of the target region as the reconstructed signal in the memory; wherein the memory further stores a program executable by the image predictive decoder to: decode the encoded data of the identification information to restore the identification information; determine whether the target region is divided into the first partition and a second partition; and when the target region is divided into the first partition and the second partition, produce a prediction signal of the first partition of the target region by using the prediction information for the specified neighbouring region. decode the encoded data of the identification information to restore the identification information; determine whether the target region is divided into the first partition and a second partition; and when the target region is divided into the first partition and the second partition, produce a prediction signal of the first partition of the target region by using the prediction information for the specified neighbouring region.