A digital watermark detecting device comprises a sequence generator which generates a predetermined sequence of numbers corresponding to a watermark which is to be detected, a shift circuit which shifts the digital content in unit of a predetermined part of data in predetermined directions, and obtain a predetermined number of shifted contents, a correlation calculator which divides the digital content and the shifted contents into blocks, arranges predetermined data obtained from the blocks of the contents to form sequences of numbers for each of the digital content and the shifted contents, and calculates correlations between the predetermined sequence of numbers and the sequences of numbers, and a determination unit which determines whether the predetermined sequence of numbers exists in the digital content based on the correlations.