An additional information signal is superimposed on a video signal at a very low level so that it does not stand out on the reproduced image. Spectral spreading code sequences are generated corresponding to different predetermined parts of the video signal. Bit information signals of the additional information signal made up of plural bits are spectrally spread by the spreading codes to generate spectrally spread bit information signals corresponding to the plural bits. The spectrally spread bit information signals are superimposed on corresponding different predetermined parts of the video signal. Because high priority bit information signals of the spectrally spread additional information signal are superimposed on high priority parts of the video signal, high priority information in the additional information can be protected even if the video signal is modified.