In an audio/video/computer graphics data synchronous reproducing/synthesizing system, a demultiplexer separates a bit stream in which an audio signal, a video signal, and computer graphics data are compressed and multiplexed, into compressed audio and video signal streams, audio and video signal time reference values, and a compressed computer graphics data stream. An audio PLL generates a first decoding clock. An audio decoder decodes the audio signal. An audio memory stores the decoded audio signal. A modulator modulates the audio signal in accordance with sound source control information. A video PLL generates a second decoding clock. A video decoder decodes the video signal. A video memory stores the decoded video signal. A CG decoder decodes the computer graphics data and event time management information. A CG memory stores the decoded computer graphics data. An event generator generates an event driving instruction. A detector detects viewpoint movement of an observer. A render engine receives the video signal, the computer graphics data, the event driving instruction, and viewpoint movement data and outputs a synthesized image of the video signal and the computer graphics data and the sound source control information. The method for this system is also disclosed.