A data processing device for burying additional information in coded data created by encoding image data and correctly reproducing the image data and the additional data from the coded data without increasing the amount of coded data. A burying compression-encoder (11) encodes image data according to a predetermined encoding rule and destroys the encoding rule according to the additional information so as to bury the additional information. A decoder (12) restores burying coded data generated by burying the additional information in the coded data to the coded data encoded according to the encoding rule, and thereby the additional information is decoded and the coded data is decoded to image data.