Abstract: RGB signals and sync signals H and V are inputted from a personal computer or the like. Additional information is superimposed to a vertical blanking period of the R signal. A timing generating unit generates a sampling pulse on the basis of the sync signals. A data extracting unit extracts the additional information by using the pulse. Processes such as discrimination of a category of the additional information and a parity check are executed by an information decoding unit. A converter converts the RGB signals into an NTSC signal. VBI data and a copy prevention signal are formed in response to a decoded result of the information decoding unit. The VBI data and copy prevention signal are superimposed to the NTSC signal in adders.