However, when there is a change, the resampling unit 440 outputs watermark wr(n) of which the length is resampled from ??? to ???. [0068] A process for removing unnecessary information generated through the correlation of watermarks made by the above process will be expressed using equations as follows: [0069] Watemark-embedded digital signals smj(n) 3 and smj+1(n) 4 adjacent to smj(n) 3 output fr