1. A digital watermark embedding apparatus including a processor, the digital watermark embedding apparatus comprising: an acquisition unit to acquire a topological invariant as digital watermark information, key information corresponding to the digital watermark information, and a target content in which the digital watermark information is to be embedded; a function generation unit coupled to the acquisition unit, the function generation unit being configured to generate a topological function corresponding to the topological invariant; a function randomization unit coupled to the function generation unit, the function randomization unit being configured to generate, based on the key information, a randomizing function, map each block of the target content to a target space based on the randomizing function, the target space comprising embedding amounts, and compute a composite function based on the randomizing function and the topological function; and a function-embedding unit coupled to the function randomization unit, the function-embedding unit being configured to embed the digital watermark information in the target content based on the composite function, wherein the target content is restored even if the target content with embedded digital watermark information is subjected to geometrical distortion.