In a signal processing device and its method as well as a program storing medium, psychological auditory sense analysis of the survival state of an input signal of the time when the input signal has been compressed is performed in response to the compression processing, and the result of the very analysis is outputted as the psychological auditory sense encoded information, and digital watermarking information is superimposed on the input signal on the basis of the psychological auditory sense encoded information, so that it is possible to easily realize digital watermarking information that has large compression resistance and digital watermarking information that has small compression resistance.