To restrain an image from deteriorating in quality between decoding and encoding when MPEG-2 data on which letter and image data are superimposed are encoded again to MPEG-2 data.

A video decoder 4 is equipped with a function to output the encoding parameter 105 of a decoded MPEG-2 stream to a video encoder 6. A superimpose 5 is equipped with a circuit detecting a superimposed region and outputs a superimposed region discriminating signal 108 to a video encoder 5. The video encoder 6 appropriately switches the encoding parameter 105 of the decoded MPEG stream obtained from the MPEG-2 stream by the use of the superimposed region discriminating signal 108, and an encoding parameter obtained in the video encoder 6 in accordance with the superimposed region discriminating signal 108 and carries out encoding. Therefore, letter and image data can be superimposed, reducing deterioration of an image in quality to an irreducible minimum.