A bytecode processing unit provided in a playback device is platform unit 20 that reads and runs a bytecode application recorded on read-only medium 105. The playback device includes: playback control unit 10 for controlling AV playback of digital streams; and machine unique function control unit 33 for performing machine unique functions unique to the playback device, to perform a control onto a content. APIs used by the bytecode application include API for playback control function, and API for socket communication. When the bytecode application requests playback control unit 10 to control the playback, it calls the playback control API to can instruct playback control unit 10 to execute the process. When the bytecode application requests execution of a machine unique function of the playback device, it instructs a machine unique function control unit to perform the process via a function call by the socket communication API.