To superimpose the data of a copyright or the like on input signals to be analyzed difficultly without degrading the quality by burying input data in coefficient data obtained by orthogonally transforming the input signals and performing an inverse orthogonal transformation processing.

In a manufacture process of an optical disk, signals DA1 are inputted to a watermark encoder 2 and converted to frequency spectrum signals DS by an MPCT calculation part 12, a representative value P for correctly indicating a level regardless of the phase change of the DA1 is obtained by a representative calculation part 14, and copyright data DC are buried to the P of the value equal to or more than 2n by a bit operation part 15. At the time, an offset is set to a prescribed bit so as to correctly reproduce a logical value even in the case of a quantization error at the time of DC reproduction, inputted to a spectrum correction part 16 together with the DS as correction data P1 and arithmetically processed and the change portion of the P is proportionally distributed in accordance with the respective spectrum values. In such a manner, the DC is buried only in the case that the P is equal to or more than a prescribed value, sound quality degradation is evaded, the DC is dispersed and the secrecy is improved.