A contents border detection apparatus and monitoring method. The apparatus comprises a digital watermark detector for detecting a digital watermark embedded in contents for which a time element is provided; and a border detector for detecting border locations for the contents corresponding to the state of the digital watermark detected by the digital watermark detector. The border detector includes a first border specification device for specifying the border locations for the contents based on information, written in the digital watermark, that is detected by the digital watermark detector and includes a second border specification device for specifying the border locations for the contents based on bit patterns embedded as the digital watermark. The border locations for the contents are detected by using the process result obtained both by the first and the second border specification devices.