By a program process, CPU 31 embeds a watermark data into a waveform data stored in wave memory 41a. The program includes a step for detecting a characterizing part (attack part and loop part) of a waveform data that represents a waveform of a musical tone where the characterizing part represents characteristics of the musical tone, and a step for embedding a watermark data into a part of the waveform data excluding the detected characterizing part. Further, CPU 31 can also extract the watermark data by a program process including a step for detecting the characterizing part and a step for extracting the watermark data embedded in a part excluding the detected characterizing part. Thus, from waveform data including a watermark data, natural musical tones can be reproduced without deteriorating the characteristics of the musical tones at the time of reproduction.