To prevent a reproduced video or audio information from being duplicated by restoring original encoded video or the audio information by decoding it when ciphered video or audio information is inputted and obtaining the video or audio information into outputted video or audio information by superposing electronic watermark information showing prohibition of duplication when the deciphered encoded-video or audio information is decoded.

In the case of a ciphered dick, deciphered encoded data is selected by a cipher decoder 10, in the case of a disk which is not ciphered, encoded data to be supplied from a reading circuit is selected and supplied to a decoding circuit 20. Dynamic image data is decoded by a decoding processing based on an MPEG 2 system by the decoding circuit 20. The decoded dynamic image data is outputted from a decoded data output terminal 80 and the electronic watermark showing the prohibition of duplication is superposed on the data by superposition 30 of the electric watermark. The electronic watermark is judged whether it is superposed on the moving image to be outputted from the decoded data output terminal 80 or not according to a condition by judgment 130 of superposition.