In a first inter-image prediction mode in which information on a motion vector is used, a first mode detection unit constructs a first candidate list from a plurality of reference block candidates based on a first predetermined order, assigns indices for designating reference block candidates added in the first candidate list, and outputs the indices of the plurality of reference candidate blocks. In a second inter-image prediction mode in which is used a motion vector difference between a motion vector predictor based on information on a motion vector, and a motion vector of a coding target block, a second mode detection unit constructs a second candidate list from a plurality of reference block candidates based on a second predetermined order, assigns indices for designating reference block candidates added in the second candidate list, and outputs the indices of the plurality of reference block candidates and motion vector differences.