In the present invention, a click sound corresponding to key depression speed is generated, and the production timings of fundamental and harmonic components respectively corresponding to each footage are changed to vary from one another in accordance with a wait time, whereby the fundamental and the harmonic components to be synthesized by additive synthesis are changed to differ from one another. Next, a click sound corresponding to key release speed is generated, and the stop timings of the fundamental and harmonic components are changed to vary from one another in accordance with a wait time, whereby the fundamental and the harmonic components to be muted are changed to differ from one another. Accordingly, by the click sound being mixed with the drawbar sound having these slight tone changes, a unique drawbar sound such as that generated by the sound producing mechanism of an actual drawbar organ is generated.