In order to prevent content data from being illegally recorded or reproduced, information for detecting that the content data is illegally distributed or recorded is added to watermark information or other information. Two sets of WM (watermark) data, a WM1 data set and a WM2 data set are prepared. For the WM1 data, data representing that the content data is package media data or distribution data, SCMS information, data representing that the content data is recorded in a disk or a semiconductor memory, and data representing the type of disk or semiconductor memory are set. For the WM2 data, the distribution time or the year and date is set as time information representing time when the content data is recorded. According to the WM1 or WM2 data, a data reproducing device (1) controls reproduction most suitably as copyright holder's intention.