The data processor of the present invention can play back video and audio synchronously from an optical disk, on which video and audio data are stored in different areas. Each area consists of one or more unit areas. The data processor includes: a playback control section for giving instructions on how to read the video and audio data and how to play back the video and audio based on the read data; a head for reading the data from one of the unit areas after another in accordance with the instructions; and audio and video buffers for retaining the audio and video data read. The playback control section instructs that the audio data be read from a predetermined one of the unit areas to the audio buffer memory, and then instructs that the video data, which is to be played back over first and second periods of time, be read from a number n (where n is an integer equal to or greater than two) of unit areas to the video buffer. The first period of time is (n+2) times as long as the maximum amount of time to move the head, and the second period of time is taken to read the audio data from the next unit area.