1. A moving picture decoding method, carried out by a computing system, including a prediction mode, comprising: in a prediction mode in which prediction mode motion vector information of a current block in a current frame has not been transmitted from an encoding side: selecting, from among multiple candidate reference frames, a frame(s) to be referenced to in the prediction mode; and determining motion vector information to be used in the prediction mode, wherein in the determining of the motion vector information, in a case when all of predetermined candidate blocks within a current frame adjacent to a current block are located outside of the screen, a zero vector is set as a motion vector for the current block; and performing prediction processing using the selected reference frame and the zero vector.