For conversion of a first video signal into a second video signal of a different format, a second auxiliary data packet is generated from a header carrying location data for multiplexing a first auxiliary data packet and main data of a first auxiliary data packet in the first video signal, and is multiplexed with the second video signal. For conversion from the second video signal into the first video signal, the first auxiliary data packet is generated from the header and the main data of the second auxiliary data packet, and multiplexed at the location determined by the location data in the first video signal.