In motion vector prediction encoding, the efficiency of motion vector prediction is improved and the efficiency of moving picture encoding is improved. A motion search is performed for a block to be encoded in a picture to be encoded using an encoded reference picture to calculate a motion vector. A plurality of blocks which include at least one of encoded blocks in the picture to be encoded and encoded blocks in an encoded picture and in predetermined positions relative to the position of the block to be encoded in the picture to be encoded are set as primary candidate blocks, and N primary candidate reference motion vectors are determined from motion vectors used in encoding the primary candidate blocks. The degrees of reliability of the primary candidate reference motion vectors which quantitatively represent effectiveness in motion vector prediction of the block to be encoded is calculated using encoded picture information for each of the primary candidate reference motion vectors. Top M primary candidate reference motion vectors with higher degrees of reliability are selected from the primary candidate reference motion vectors as secondary candidate reference motion vectors. A predictive motion vector of the block to be encoded is calculated using the secondary candidate reference motion vectors, and a residual between the motion vector obtained through the motion search of the block to be encoded and the predictive motion vector is encoded as encoded information of the motion vector.