To conduct more proper error compensation in the case that only a motion vector for backward referring is available for motion vectors to be used for error compensation.

In the case of decoding a coded image signal by a decoder 10, when a motion vector stored in a macro block is a backward referring motion vector, a characterizing processing unit 18 characterizes the motion vector and the result is stored in a concealment motion vector storage device 12. In the case of conducting error processing, a discrimination device 20 discriminates whether a motion vector to generate a substitute macro block is a backward referring vector or a forward referring block. When the motion vector is a backward referring vector, the substitute macro block is extracted from a backward referring frame according to the backward referring motion vector.