1. A video decoding method comprising the steps of: calculating a predictive motion vector; calculating a motion vector by summing the predictive motion vector calculated in the predictive motion vector calculating step and a differential motion vector decoded from a coded stream; and performing an inter-prediction process using the motion vector calculated in the motion vector calculating step, wherein the predictive motion vector calculating step includes: a first process to retrieve selection information that is an added bit from the coded stream; a second process to select a plurality of candidate blocks among blocks decoded prior to a block to be decoded, a third process to use any one of a first value and a second value when the first value is equal to the second value in motion vector values of the plurality of candidate blocks, and a fourth process to read out the selection information for selecting one motion vector value among a plurality of motion vector values including the motion vector value of the first value or the second value selected in the third process and a motion vector value other than the first value and the second value in the motion vector values of the plurality of candidate blocks selected in the second process, and to select a predictive motion vector based on the selection information, wherein the one motion vector value selected from the plurality of motion vector values is determined based on the selection information regardless of the differential motion vector, and wherein the candidate block has peripheral blocks included in the same frame as the block to be decoded and blocks included in a different frame from the block to be decoded.