To provide an information embedding system to a acoustic signal, capable of embedding many pieces of information by setting an optimum threshold which is not fixed but variable for each frame, while enhancing extraction accuracy.

In the case that a bit value is imbedded in a frame having low-frequency intensity of E1 and E2, which is larger than the threshold "Lev" (a), embedding process is executed by an embedding means and the embedded bit value is recorded as an embedding log (b). An extracting/collating means executes extracting process (c) and refers to the embedding log, and when the extracted bit value and a content of the embedding log are different, it is recorded as an extracting log as one that inhibits bit embedding in the frame (d). The embedding means executes the embedding process on the frame where imbedding is inhibited, in accordance with the extraction log (e).