A relay apparatus, comprises a reception section that receives real-time data, a monitoring section that periodically detects quality of a transmission path to be used for transmitting the real-time data toward a destination thereof, a determination section that determines a length of an interleaving cycle according to the quality of the transmission path, an interleaving section that interleaves the real-time data in the interleaving cycle having the determined length, and a transmission section that transmits the interleaved real-time data to the transmission path.