1. A data processing apparatus configured to output picture data to a reproduction apparatus configured to reproduce a plurality of picture data, the data processing apparatus comprising: a processing circuit configured to output, to said reproduction apparatus, said picture data in an order in accordance with a reproduction direction designated at said reproduction apparatus, to designate an address in an input memory at which said picture data output to said reproduction apparatus is to be written, to output an address notification that indicates said address to said reproduction apparatus, and to manage said picture data stored in said input memory based on commands output to said reproduction apparatus including a command to reverse said reproduction direction at said reproduction apparatus; and if said reproduction direction designated at said reproduction apparatus is reversed by a command output by said processing circuit to said reproduction apparatus, said processing circuit is configured to judge whether said picture data to be used next in reproduction in said reproduction direction after reversal is stored in said input memory, and to output said picture data to be used next in reproduction in said reproduction direction after reversal to said reproduction apparatus conditional on said picture data to be used next in reproduction by said reproduction direction after reversal being judged as not being stored in said input memory.