The syntax for expressing the prediction mode of the coding block will be described with reference to FIGS. 12A, 12B, and 13. The pred_mode_flag in FIG. 12A is a flag indicating whether the mode is inter prediction. Setting of pred_mode_flag 0 indicates inter prediction while setting of pred_mode_flag 1 indicates intra prediction. Information of intra prediction intra_pred_mode is transmitted in the case of intra prediction, while merge_flag is transmitted in the case of inter prediction. merge_flag is a flag indicating whether the mode to use is the merge mode or the motion vector predictor mode. In the case of the motion vector predictor mode (merge_flag=0), a flag inter_affine_flag indicating whether to apply the subblock motion vector predictor mode is transmitted. In the case of applying the subblock motion vector predictor mode (inter_affine_flag=1), cu_affine_type_flag is transmitted. cu_affine_type_flag is a flag for determining the number of control points in the subblock motion vector predictor mode.
